diff --git a/src/main/java/com/stripe/net/ApiRequestParams.java b/src/main/java/com/stripe/net/ApiRequestParams.java
index 7605de640b5..b40c3c34bed 100644
--- a/src/main/java/com/stripe/net/ApiRequestParams.java
+++ b/src/main/java/com/stripe/net/ApiRequestParams.java
@@ -1,16 +1,5 @@
 package com.stripe.net;
 
-import com.google.gson.FieldNamingPolicy;
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-import com.google.gson.JsonObject;
-import com.google.gson.TypeAdapter;
-import com.google.gson.TypeAdapterFactory;
-import com.google.gson.reflect.TypeToken;
-import com.google.gson.stream.JsonReader;
-import com.google.gson.stream.JsonWriter;
-
-import java.io.IOException;
 import java.util.Map;
 
 /**
@@ -23,70 +12,34 @@ public abstract class ApiRequestParams {
   /**
    * Interface implemented by all enum parameter to get the actual string value that Stripe API
    * expects. Internally, it used in custom serialization
-   * {@link ApiRequestParams.HasEmptyEnumTypeAdapterFactory} converting empty string enum to null.
+   * {@link ApiRequestParamsConverter} converting empty string enum to
+   * null.
    */
   public interface EnumParam {
     String getValue();
   }
 
-  private static final Gson GSON = new GsonBuilder()
-      .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
-      .registerTypeAdapterFactory(new HasEmptyEnumTypeAdapterFactory())
-      .create();
-
-  private static final UntypedMapDeserializer UNTYPED_MAP_DESERIALIZER =
-      new UntypedMapDeserializer();
-
-  private static class HasEmptyEnumTypeAdapterFactory implements TypeAdapterFactory {
-    @SuppressWarnings("unchecked")
-    @Override
-    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
-      if (!EnumParam.class.isAssignableFrom(type.getRawType())) {
-        return null;
-      }
-
-      TypeAdapter<EnumParam> paramEnum = new TypeAdapter<EnumParam>() {
-        @Override
-        public void write(JsonWriter out, EnumParam value) throws IOException {
-          if (value.getValue().equals("")) {
-            // need to restore serialize null setting
-            // not to affect other fields
-            boolean previousSetting = out.getSerializeNulls();
-            out.setSerializeNulls(true);
-            out.nullValue();
-            out.setSerializeNulls(previousSetting);
-          } else {
-            out.value(value.getValue());
-          }
-        }
+  /**
+   * Param key for an `extraParams` map. Any param/sub-param specifying a field
+   * intended to support extra params from users should have the annotation
+   * {@code @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)}. Logic to handle this is in
+   * {@link ApiRequestParamsConverter}.
+   */
+  public static final String EXTRA_PARAMS_KEY = "_stripe_java_extra_param_key";
 
-        @Override
-        public EnumParam read(JsonReader in) {
-          throw new UnsupportedOperationException(
-              "No deserialization is expected from this private type adapter for enum param.");
-        }
-      };
-      return (TypeAdapter<T>) paramEnum.nullSafe();
-    }
-  }
+  /**
+   * Converter mapping typed API request parameters into an untyped map.
+   */
+  private static final ApiRequestParamsConverter PARAMS_CONVERTER =
+      new ApiRequestParamsConverter();
 
   /**
-   * Convenient method to convert this typed request params into an untyped map. This map is
-   * composed of {@code Map<String, Object>}, {@code List<Object>}, and basic Java data types.
-   * This allows you to test building the request params and verify compatibility with your
-   * prior integrations using the untyped params map
-   * {@link ApiResource#request(ApiResource.RequestMethod, String, Map, Class, RequestOptions)}.
-   *
-   * <p>The peculiarity of this conversion is that `EMPTY` {@link EnumParam} with raw
-   * value of empty string will be converted to null. This is compatible with the existing
-   * contract enforcing no empty string in the untyped map params.
-   *
-   * <p>Because of the translation from `EMPTY` enum to null, deserializing this map back to a
-   * request instance is lossy. The null value will not be converted back to the `EMPTY` enum.
+   * Convert `this` api request params to an untyped map. The conversion is specific to api
+   * request params object. Please see documentation in
+   * {@link ApiRequestParamsConverter#convert(ApiRequestParams)}.
    */
   public Map<String, Object> toMap() {
-    JsonObject json = GSON.toJsonTree(this).getAsJsonObject();
-    return UNTYPED_MAP_DESERIALIZER.deserialize(json);
+    return PARAMS_CONVERTER.convert(this);
   }
 }
 
diff --git a/src/main/java/com/stripe/net/ApiRequestParamsConverter.java b/src/main/java/com/stripe/net/ApiRequestParamsConverter.java
new file mode 100644
index 00000000000..0f4e7bd8cfa
--- /dev/null
+++ b/src/main/java/com/stripe/net/ApiRequestParamsConverter.java
@@ -0,0 +1,148 @@
+package com.stripe.net;
+
+import com.google.gson.FieldNamingPolicy;
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.TypeAdapter;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+
+import com.stripe.Stripe;
+import com.stripe.param.common.EmptyParam;
+
+import java.io.IOException;
+import java.util.Map;
+
+/**
+ * Converter to map an api request object to an untyped map.
+ * It is not called a *Serializer because the outcome is not a JSON data.
+ * It is not called *UntypedMapDeserializer because it is not converting from JSON.
+ */
+class ApiRequestParamsConverter {
+  /**
+   * Strategy to flatten extra params in the API request parameters.
+   */
+  private static class ExtraParamsFlatteningStrategy implements UntypedMapDeserializer.Strategy {
+    @Override
+    public void deserializeAndTransform(Map<String, Object> outerMap,
+                                        Map.Entry<String, JsonElement> jsonEntry,
+                                        UntypedMapDeserializer untypedMapDeserializer) {
+      String key = jsonEntry.getKey();
+      JsonElement jsonValue = jsonEntry.getValue();
+      if (ApiRequestParams.EXTRA_PARAMS_KEY.equals(key)) {
+        if (!jsonValue.isJsonObject()) {
+          throw new IllegalStateException(String.format(
+              "Unexpected schema for extra params. JSON object is expected at key `%s`, but found"
+                  + " `%s`. This is likely a problem with this current library version `%s`. "
+                  + "Please contact support@stripe.com for assistance.",
+              ApiRequestParams.EXTRA_PARAMS_KEY, jsonValue, Stripe.VERSION));
+        }
+        // JSON value now corresponds to the extra params map, and is also deserialized as a map.
+        // Instead of putting this result map under the original key, flatten the map
+        // by adding all its key/value pairs to the outer map instead.
+        Map<String, Object> extraParamsMap =
+            untypedMapDeserializer.deserialize(jsonValue.getAsJsonObject());
+        for (Map.Entry<String, Object> entry : extraParamsMap.entrySet()) {
+          validateDuplicateKey(outerMap, entry.getKey(), entry.getValue());
+          outerMap.put(entry.getKey(), entry.getValue());
+        }
+      } else {
+        Object value = untypedMapDeserializer.deserializeJsonElement(jsonValue);
+        validateDuplicateKey(outerMap, key, value);
+
+        // Normal deserialization where output map has the same structure as the given JSON content.
+        // The deserialized content is an untyped `Object` and added to the outer map at the
+        // original key.
+        outerMap.put(key, value);
+      }
+    }
+  }
+
+  private static void validateDuplicateKey(Map<String, Object> outerMap,
+                                           String paramKey, Object paramValue) {
+    if (outerMap.containsKey(paramKey)) {
+      throw new IllegalArgumentException(String.format(
+          "Found multiple param values for the same param key. This can happen because you passed "
+              + "additional parameters via `putExtraParam` that conflict with the existing params. "
+              + "Found param key `%s` with values `%s` and `%s`. "
+              + "If you wish to pass additional params for nested parameters, you "
+              + "should add extra params at the nested params themselves, not from the "
+              + "top-level param.",
+          paramKey, outerMap.get(paramKey), paramValue));
+    }
+  }
+
+  /**
+   * Type adapter to convert an empty enum to null value to comply with the lower-lever encoding
+   * logic for the API request parameters.
+   */
+  private static class HasEmptyEnumTypeAdapterFactory implements TypeAdapterFactory {
+    @SuppressWarnings("unchecked")
+    @Override
+    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
+      if (!ApiRequestParams.EnumParam.class.isAssignableFrom(type.getRawType())) {
+        return null;
+      }
+
+      TypeAdapter<ApiRequestParams.EnumParam> paramEnum =
+          new TypeAdapter<ApiRequestParams.EnumParam>() {
+            @Override
+            public void write(JsonWriter out, ApiRequestParams.EnumParam value) throws IOException {
+              if (value.getValue().equals("")) {
+                // need to restore serialize null setting
+                // not to affect other fields
+                boolean previousSetting = out.getSerializeNulls();
+                out.setSerializeNulls(true);
+                out.nullValue();
+                out.setSerializeNulls(previousSetting);
+              } else {
+                out.value(value.getValue());
+              }
+            }
+
+            @Override
+            public ApiRequestParams.EnumParam read(JsonReader in) {
+              throw new UnsupportedOperationException(
+                  "No deserialization is expected from this private type adapter for enum param.");
+            }
+          };
+      return (TypeAdapter<T>) paramEnum.nullSafe();
+    }
+  }
+
+  private static final Gson GSON = new GsonBuilder()
+      .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
+      .registerTypeAdapterFactory(new ApiRequestParamsConverter.HasEmptyEnumTypeAdapterFactory())
+      .create();
+
+  private static final UntypedMapDeserializer FLATTENING_EXTRA_PARAMS_DESERIALIZER =
+      new UntypedMapDeserializer(new ExtraParamsFlatteningStrategy());
+
+  /**
+   * Convert the given request params into an untyped map. This map is
+   * composed of {@code Map<String, Object>}, {@code List<Object>}, and basic Java data types.
+   * This allows you to test building the request params and verify compatibility with your
+   * prior integrations using the untyped params map
+   * {@link ApiResource#request(ApiResource.RequestMethod, String, Map, Class, RequestOptions)}.
+   *
+   * <p>There are two peculiarities in this conversion:
+   *
+   * <p>1) {@link EmptyParam#EMPTY}, containing a raw empty string value, is converted to null.
+   * This is because the form-encoding layer prohibits passing empty string as a param map value.
+   * It, however, allows a null value in the map (present key but null value).
+   * Because of the translation from `EMPTY` enum to null, deserializing this map back to a
+   * request instance is lossy. The null value will not be converted back to the `EMPTY` enum.
+   *
+   * <p>2) Parameter with serialized name {@link ApiRequestParams#EXTRA_PARAMS_KEY} will be
+   * flattened. This is to support passing new params that the current library has not
+   * yet supported.
+   */
+  Map<String, Object> convert(ApiRequestParams apiRequestParams) {
+    JsonObject jsonParams = GSON.toJsonTree(apiRequestParams).getAsJsonObject();
+    return FLATTENING_EXTRA_PARAMS_DESERIALIZER.deserialize(jsonParams);
+  }
+}
diff --git a/src/main/java/com/stripe/net/UntypedMapDeserializer.java b/src/main/java/com/stripe/net/UntypedMapDeserializer.java
index c328e1f2554..997898f3894 100644
--- a/src/main/java/com/stripe/net/UntypedMapDeserializer.java
+++ b/src/main/java/com/stripe/net/UntypedMapDeserializer.java
@@ -17,28 +17,95 @@
  * JSON representation (using GSON) to a generic {@code Map<String, Object>}.
  */
 public class UntypedMapDeserializer {
+  /**
+   * Strategy to deserialize a JSON element, allowing for custom interactions between the
+   * deserialized element and its outer map.
+   * For example, for a full JSON:
+   * {
+   *   "foo": 1,
+   *   "foo_inner": { // outer context map
+   *     "bar": 1,
+   *     "zing": 2,   // given JSON element
+   *   },
+   * }
+   *
+   * <p>Given, a json entry of "zing": 2, the outer map corresponds to value for "foo_inner". A
+   * default strategy is to simply deserialize value and puts it at "zing" key in the outer map.
+   *
+   * <p>Custom strategy allows, for example, renaming the key "zing", wrapping the deserialized
+   * value in another map/array, or flattening the value if the deserialized value is a map.
+   */
+  interface Strategy {
+    /**
+     * Define how the given JSON element should be deserialized, and how the deserialized content
+     * should be added to the given outer map.
+     * @param outerMap               the untyped map that the deserialized content can be added to.
+     * @param jsonEntry              original JSON entry with key and json element
+     * @param untypedMapDeserializer deserializer for the untyped map to transform the given json
+     *                               element
+     */
+    void deserializeAndTransform(Map<String, Object> outerMap,
+                                 Map.Entry<String, JsonElement> jsonEntry,
+                                 UntypedMapDeserializer untypedMapDeserializer
+    );
+  }
+
+  /**
+   * Strategy for this deserializer.
+   */
+  private Strategy strategy;
+
+  /**
+   * Default deserializer for the untyped map. The result untyped map has same object graph
+   * structure as that of the given JSON content.
+   */
+  public UntypedMapDeserializer() {
+    /**
+     * Default strategy where each JSON element gets deserialized and added with its original key.
+     */
+    this.strategy = new Strategy() {
+      @Override
+      public void deserializeAndTransform(Map<String, Object> outerMap,
+                                          Map.Entry<String, JsonElement> jsonEntry,
+                                          UntypedMapDeserializer untypedMapDeserializer) {
+        outerMap.put(
+            jsonEntry.getKey(),
+            untypedMapDeserializer.deserializeJsonElement(jsonEntry.getValue()));
+      }
+    };
+  }
+
+  /**
+   * Deserializer with a custom strategy.
+   * @param strategy definition of how JSON element should be deserialized and set in its outer map.
+   */
+  UntypedMapDeserializer(Strategy strategy) {
+    this.strategy = strategy;
+  }
+
   /**
    * Deserialize JSON into untyped map.
    * {@code JsonArray} is represented as {@code List<Object>}.
    * {@code JsonObject} is represented as {@code Map<String, Object>}.
    * {@code JsonPrimitive} is represented as String, Number, or Boolean.
-   *
    * @param jsonObject  JSON to convert into untyped map
    * @return untyped map without dependency on JSON representation.
    */
   public Map<String, Object> deserialize(JsonObject jsonObject) {
     Map<String, Object> objMap = new HashMap<>();
     for (Map.Entry<String, JsonElement> entry : jsonObject.entrySet()) {
-      String key = entry.getKey();
-      JsonElement element = entry.getValue();
-      // JsonElement is super class of all JSON standard types:
-      // array, null, primitive, and object
-      objMap.put(key, deserializeJsonElement(element));
+      this.strategy.deserializeAndTransform(objMap, entry, this);
     }
     return objMap;
   }
 
-  private Object deserializeJsonElement(JsonElement element) {
+  /**
+   * Normalizes JSON element into an untyped Object as value to the untyped map.
+   * @param element JSON element to convert to java Object
+   * @return untyped object, one of {@code Map<String, Object>}, {@code String}, {@code Number},
+   * {@code Boolean}, or {@code List<Array>}.
+   */
+  Object deserializeJsonElement(JsonElement element) {
     if (element.isJsonNull()) {
       return null;
     } else if (element.isJsonObject()) {
diff --git a/src/main/java/com/stripe/param/AccountCreateParams.java b/src/main/java/com/stripe/param/AccountCreateParams.java
index 2397fa7dc39..3493dbece55 100644
--- a/src/main/java/com/stripe/param/AccountCreateParams.java
+++ b/src/main/java/com/stripe/param/AccountCreateParams.java
@@ -74,6 +74,15 @@ public class AccountCreateParams extends ApiRequestParams {
   @SerializedName("external_account")
   String externalAccount;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Information about the person represented by the account. This field is null unless
    * `business_type` is set to `individual`.
@@ -124,6 +133,7 @@ private AccountCreateParams(
       String email,
       List<String> expand,
       String externalAccount,
+      Map<String, Object> extraParams,
       Individual individual,
       Map<String, String> metadata,
       List<RequestedCapability> requestedCapabilities,
@@ -139,6 +149,7 @@ private AccountCreateParams(
     this.email = email;
     this.expand = expand;
     this.externalAccount = externalAccount;
+    this.extraParams = extraParams;
     this.individual = individual;
     this.metadata = metadata;
     this.requestedCapabilities = requestedCapabilities;
@@ -170,6 +181,8 @@ public static class Builder {
 
     private String externalAccount;
 
+    private Map<String, Object> extraParams;
+
     private Individual individual;
 
     private Map<String, String> metadata;
@@ -194,6 +207,7 @@ public AccountCreateParams build() {
           this.email,
           this.expand,
           this.externalAccount,
+          this.extraParams,
           this.individual,
           this.metadata,
           this.requestedCapabilities,
@@ -304,6 +318,32 @@ public Builder setExternalAccount(String externalAccount) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AccountCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AccountCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Information about the person represented by the account. This field is null unless
      * `business_type` is set to `individual`.
@@ -391,6 +431,15 @@ public Builder setType(Type type) {
   }
 
   public static class BusinessProfile {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The merchant category code for the account. MCCs are used to classify businesses based on the
      * goods or services they provide.
@@ -426,6 +475,7 @@ public static class BusinessProfile {
     String url;
 
     private BusinessProfile(
+        Map<String, Object> extraParams,
         String mcc,
         String name,
         String productDescription,
@@ -433,6 +483,7 @@ private BusinessProfile(
         String supportPhone,
         String supportUrl,
         String url) {
+      this.extraParams = extraParams;
       this.mcc = mcc;
       this.name = name;
       this.productDescription = productDescription;
@@ -447,6 +498,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String mcc;
 
       private String name;
@@ -464,6 +517,7 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public BusinessProfile build() {
         return new BusinessProfile(
+            this.extraParams,
             this.mcc,
             this.name,
             this.productDescription,
@@ -473,6 +527,32 @@ public BusinessProfile build() {
             this.url);
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountCreateParams.BusinessProfile#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountCreateParams.BusinessProfile#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * The merchant category code for the account. MCCs are used to classify businesses based on
        * the goods or services they provide.
@@ -546,6 +626,15 @@ public static class Company {
     @SerializedName("directors_provided")
     Boolean directorsProvided;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The company's legal name. */
     @SerializedName("name")
     String name;
@@ -591,6 +680,7 @@ private Company(
         AddressKana addressKana,
         AddressKanji addressKanji,
         Boolean directorsProvided,
+        Map<String, Object> extraParams,
         String name,
         String nameKana,
         String nameKanji,
@@ -603,6 +693,7 @@ private Company(
       this.addressKana = addressKana;
       this.addressKanji = addressKanji;
       this.directorsProvided = directorsProvided;
+      this.extraParams = extraParams;
       this.name = name;
       this.nameKana = nameKana;
       this.nameKanji = nameKanji;
@@ -626,6 +717,8 @@ public static class Builder {
 
       private Boolean directorsProvided;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String nameKana;
@@ -649,6 +742,7 @@ public Company build() {
             this.addressKana,
             this.addressKanji,
             this.directorsProvided,
+            this.extraParams,
             this.name,
             this.nameKana,
             this.nameKanji,
@@ -689,6 +783,32 @@ public Builder setDirectorsProvided(Boolean directorsProvided) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountCreateParams.Company#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountCreateParams.Company#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The company's legal name. */
       public Builder setName(String name) {
         this.name = name;
@@ -758,6 +878,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Address line 1 (e.g., street, PO Box, or company name). */
       @SerializedName("line1")
       String line1;
@@ -777,12 +906,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -798,6 +929,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -809,7 +942,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         /** City, district, suburb, town, or village. */
@@ -827,6 +966,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Company.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Company.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Address line 1 (e.g., street, PO Box, or company name). */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -865,6 +1032,15 @@ public static class AddressKana {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Block or building number. */
       @SerializedName("line1")
       String line1;
@@ -888,6 +1064,7 @@ public static class AddressKana {
       private AddressKana(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
@@ -895,6 +1072,7 @@ private AddressKana(
           String town) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -911,6 +1089,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -926,6 +1106,7 @@ public AddressKana build() {
           return new AddressKana(
               this.city,
               this.country,
+              this.extraParams,
               this.line1,
               this.line2,
               this.postalCode,
@@ -948,6 +1129,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Company.AddressKana#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Company.AddressKana#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Block or building number. */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -992,6 +1201,15 @@ public static class AddressKanji {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Block or building number. */
       @SerializedName("line1")
       String line1;
@@ -1015,6 +1233,7 @@ public static class AddressKanji {
       private AddressKanji(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
@@ -1022,6 +1241,7 @@ private AddressKanji(
           String town) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -1038,6 +1258,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -1053,6 +1275,7 @@ public AddressKanji build() {
           return new AddressKanji(
               this.city,
               this.country,
+              this.extraParams,
               this.line1,
               this.line2,
               this.postalCode,
@@ -1075,6 +1298,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Company.AddressKanji#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Company.AddressKanji#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Block or building number. */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -1128,6 +1379,15 @@ public static class Individual {
     @SerializedName("email")
     String email;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The individual's first name. */
     @SerializedName("first_name")
     String firstName;
@@ -1196,6 +1456,7 @@ private Individual(
         AddressKanji addressKanji,
         Dob dob,
         String email,
+        Map<String, Object> extraParams,
         String firstName,
         String firstNameKana,
         String firstNameKanji,
@@ -1214,6 +1475,7 @@ private Individual(
       this.addressKanji = addressKanji;
       this.dob = dob;
       this.email = email;
+      this.extraParams = extraParams;
       this.firstName = firstName;
       this.firstNameKana = firstNameKana;
       this.firstNameKanji = firstNameKanji;
@@ -1244,6 +1506,8 @@ public static class Builder {
 
       private String email;
 
+      private Map<String, Object> extraParams;
+
       private String firstName;
 
       private String firstNameKana;
@@ -1278,6 +1542,7 @@ public Individual build() {
             this.addressKanji,
             this.dob,
             this.email,
+            this.extraParams,
             this.firstName,
             this.firstNameKana,
             this.firstNameKanji,
@@ -1322,6 +1587,32 @@ public Builder setEmail(String email) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountCreateParams.Individual#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountCreateParams.Individual#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The individual's first name. */
       public Builder setFirstName(String firstName) {
         this.firstName = firstName;
@@ -1438,6 +1729,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Address line 1 (e.g., street, PO Box, or company name). */
       @SerializedName("line1")
       String line1;
@@ -1457,12 +1757,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -1478,6 +1780,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -1489,7 +1793,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         /** City, district, suburb, town, or village. */
@@ -1507,6 +1817,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Address line 1 (e.g., street, PO Box, or company name). */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -1545,6 +1883,15 @@ public static class AddressKana {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Block or building number. */
       @SerializedName("line1")
       String line1;
@@ -1568,6 +1915,7 @@ public static class AddressKana {
       private AddressKana(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
@@ -1575,6 +1923,7 @@ private AddressKana(
           String town) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -1591,6 +1940,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -1606,6 +1957,7 @@ public AddressKana build() {
           return new AddressKana(
               this.city,
               this.country,
+              this.extraParams,
               this.line1,
               this.line2,
               this.postalCode,
@@ -1628,6 +1980,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.AddressKana#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.AddressKana#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Block or building number. */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -1672,6 +2052,15 @@ public static class AddressKanji {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Block or building number. */
       @SerializedName("line1")
       String line1;
@@ -1695,6 +2084,7 @@ public static class AddressKanji {
       private AddressKanji(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
@@ -1702,6 +2092,7 @@ private AddressKanji(
           String town) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -1718,6 +2109,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -1733,6 +2126,7 @@ public AddressKanji build() {
           return new AddressKanji(
               this.city,
               this.country,
+              this.extraParams,
               this.line1,
               this.line2,
               this.postalCode,
@@ -1755,6 +2149,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.AddressKanji#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.AddressKanji#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Block or building number. */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -1792,6 +2214,15 @@ public static class Dob {
       @SerializedName("day")
       Long day;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** The month of birth, between 1 and 12. */
       @SerializedName("month")
       Long month;
@@ -1800,8 +2231,9 @@ public static class Dob {
       @SerializedName("year")
       Long year;
 
-      private Dob(Long day, Long month, Long year) {
+      private Dob(Long day, Map<String, Object> extraParams, Long month, Long year) {
         this.day = day;
+        this.extraParams = extraParams;
         this.month = month;
         this.year = year;
       }
@@ -1813,13 +2245,15 @@ public static Builder builder() {
       public static class Builder {
         private Long day;
 
+        private Map<String, Object> extraParams;
+
         private Long month;
 
         private Long year;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Dob build() {
-          return new Dob(this.day, this.month, this.year);
+          return new Dob(this.day, this.extraParams, this.month, this.year);
         }
 
         /** The day of birth, between 1 and 31. */
@@ -1828,6 +2262,34 @@ public Builder setDay(Long day) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.Dob#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.Dob#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** The month of birth, between 1 and 12. */
         public Builder setMonth(Long month) {
           this.month = month;
@@ -1847,8 +2309,18 @@ public static class Verification {
       @SerializedName("document")
       Document document;
 
-      private Verification(Document document) {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
+      private Verification(Document document, Map<String, Object> extraParams) {
         this.document = document;
+        this.extraParams = extraParams;
       }
 
       public static Builder builder() {
@@ -1858,9 +2330,11 @@ public static Builder builder() {
       public static class Builder {
         private Document document;
 
+        private Map<String, Object> extraParams;
+
         /** Finalize and obtain parameter instance from this builder. */
         public Verification build() {
-          return new Verification(this.document);
+          return new Verification(this.document, this.extraParams);
         }
 
         /** An identifying document, either a passport or local ID card. */
@@ -1868,6 +2342,34 @@ public Builder setDocument(Document document) {
           this.document = document;
           return this;
         }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.Verification#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Individual.Verification#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
       }
 
       public static class Document {
@@ -1878,6 +2380,16 @@ public static class Document {
         @SerializedName("back")
         String back;
 
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
         /**
          * The front of an ID returned by a [file upload](#create_file) with a `purpose` value of
          * `identity_document`.
@@ -1885,8 +2397,9 @@ public static class Document {
         @SerializedName("front")
         String front;
 
-        private Document(String back, String front) {
+        private Document(String back, Map<String, Object> extraParams, String front) {
           this.back = back;
+          this.extraParams = extraParams;
           this.front = front;
         }
 
@@ -1898,11 +2411,13 @@ public static Builder builder() {
         public static class Builder {
           private String back;
 
+          private Map<String, Object> extraParams;
+
           private String front;
 
           /** Finalize and obtain parameter instance from this builder. */
           public Document build() {
-            return new Document(this.back, this.front);
+            return new Document(this.back, this.extraParams, this.front);
           }
 
           /**
@@ -1914,6 +2429,34 @@ public Builder setBack(String back) {
             return this;
           }
 
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountCreateParams.Individual.Verification.Document#extraParams} for
+           * the field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountCreateParams.Individual.Verification.Document#extraParams} for
+           * the field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
+          }
+
           /**
            * The front of an ID returned by a [file upload](#create_file) with a `purpose` value of
            * `identity_document`.
@@ -1939,6 +2482,15 @@ public static class Settings {
     @SerializedName("card_payments")
     CardPayments cardPayments;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Settings that apply across payment methods for charging on the account. */
     @SerializedName("payments")
     Payments payments;
@@ -1948,9 +2500,14 @@ public static class Settings {
     Payouts payouts;
 
     private Settings(
-        Branding branding, CardPayments cardPayments, Payments payments, Payouts payouts) {
+        Branding branding,
+        CardPayments cardPayments,
+        Map<String, Object> extraParams,
+        Payments payments,
+        Payouts payouts) {
       this.branding = branding;
       this.cardPayments = cardPayments;
+      this.extraParams = extraParams;
       this.payments = payments;
       this.payouts = payouts;
     }
@@ -1964,13 +2521,16 @@ public static class Builder {
 
       private CardPayments cardPayments;
 
+      private Map<String, Object> extraParams;
+
       private Payments payments;
 
       private Payouts payouts;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Settings build() {
-        return new Settings(this.branding, this.cardPayments, this.payments, this.payouts);
+        return new Settings(
+            this.branding, this.cardPayments, this.extraParams, this.payments, this.payouts);
       }
 
       /**
@@ -1988,6 +2548,32 @@ public Builder setCardPayments(CardPayments cardPayments) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountCreateParams.Settings#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountCreateParams.Settings#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Settings that apply across payment methods for charging on the account. */
       public Builder setPayments(Payments payments) {
         this.payments = payments;
@@ -2002,6 +2588,15 @@ public Builder setPayouts(Payouts payouts) {
     }
 
     public static class Branding {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * (ID of a [file upload](https://stripe.com/docs/guides/file-upload)) An icon for the
        * account. Must be square and at least 128px x 128px.
@@ -2021,7 +2616,9 @@ public static class Branding {
       @SerializedName("primary_color")
       String primaryColor;
 
-      private Branding(String icon, String logo, String primaryColor) {
+      private Branding(
+          Map<String, Object> extraParams, String icon, String logo, String primaryColor) {
+        this.extraParams = extraParams;
         this.icon = icon;
         this.logo = logo;
         this.primaryColor = primaryColor;
@@ -2032,6 +2629,8 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private String icon;
 
         private String logo;
@@ -2040,7 +2639,35 @@ public static class Builder {
 
         /** Finalize and obtain parameter instance from this builder. */
         public Branding build() {
-          return new Branding(this.icon, this.logo, this.primaryColor);
+          return new Branding(this.extraParams, this.icon, this.logo, this.primaryColor);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Settings.Branding#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Settings.Branding#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /**
@@ -2078,6 +2705,15 @@ public static class CardPayments {
       @SerializedName("decline_on")
       DeclineOn declineOn;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The default text that appears on credit card statements when a charge is made. This field
        * prefixes any dynamic `statement_descriptor` specified on the charge.
@@ -2087,8 +2723,10 @@ public static class CardPayments {
       @SerializedName("statement_descriptor_prefix")
       String statementDescriptorPrefix;
 
-      private CardPayments(DeclineOn declineOn, String statementDescriptorPrefix) {
+      private CardPayments(
+          DeclineOn declineOn, Map<String, Object> extraParams, String statementDescriptorPrefix) {
         this.declineOn = declineOn;
+        this.extraParams = extraParams;
         this.statementDescriptorPrefix = statementDescriptorPrefix;
       }
 
@@ -2099,11 +2737,13 @@ public static Builder builder() {
       public static class Builder {
         private DeclineOn declineOn;
 
+        private Map<String, Object> extraParams;
+
         private String statementDescriptorPrefix;
 
         /** Finalize and obtain parameter instance from this builder. */
         public CardPayments build() {
-          return new CardPayments(this.declineOn, this.statementDescriptorPrefix);
+          return new CardPayments(this.declineOn, this.extraParams, this.statementDescriptorPrefix);
         }
 
         /**
@@ -2115,6 +2755,34 @@ public Builder setDeclineOn(DeclineOn declineOn) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Settings.CardPayments#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Settings.CardPayments#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * The default text that appears on credit card statements when a charge is made. This field
          * prefixes any dynamic `statement_descriptor` specified on the charge.
@@ -2143,9 +2811,20 @@ public static class DeclineOn {
         @SerializedName("cvc_failure")
         Boolean cvcFailure;
 
-        private DeclineOn(Boolean avsFailure, Boolean cvcFailure) {
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
+        private DeclineOn(Boolean avsFailure, Boolean cvcFailure, Map<String, Object> extraParams) {
           this.avsFailure = avsFailure;
           this.cvcFailure = cvcFailure;
+          this.extraParams = extraParams;
         }
 
         public static Builder builder() {
@@ -2157,9 +2836,11 @@ public static class Builder {
 
           private Boolean cvcFailure;
 
+          private Map<String, Object> extraParams;
+
           /** Finalize and obtain parameter instance from this builder. */
           public DeclineOn build() {
-            return new DeclineOn(this.avsFailure, this.cvcFailure);
+            return new DeclineOn(this.avsFailure, this.cvcFailure, this.extraParams);
           }
 
           /**
@@ -2180,11 +2861,48 @@ public Builder setCvcFailure(Boolean cvcFailure) {
             this.cvcFailure = cvcFailure;
             return this;
           }
+
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountCreateParams.Settings.CardPayments.DeclineOn#extraParams} for
+           * the field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountCreateParams.Settings.CardPayments.DeclineOn#extraParams} for
+           * the field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
+          }
         }
       }
     }
 
     public static class Payments {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The default text that appears on credit card statements when a charge is made. This field
        * prefixes any dynamic `statement_descriptor` specified on the charge.
@@ -2192,7 +2910,8 @@ public static class Payments {
       @SerializedName("statement_descriptor")
       String statementDescriptor;
 
-      private Payments(String statementDescriptor) {
+      private Payments(Map<String, Object> extraParams, String statementDescriptor) {
+        this.extraParams = extraParams;
         this.statementDescriptor = statementDescriptor;
       }
 
@@ -2201,11 +2920,41 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private String statementDescriptor;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Payments build() {
-          return new Payments(this.statementDescriptor);
+          return new Payments(this.extraParams, this.statementDescriptor);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Settings.Payments#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Settings.Payments#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /**
@@ -2228,6 +2977,15 @@ public static class Payouts {
       @SerializedName("debit_negative_balances")
       Boolean debitNegativeBalances;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * Details on when funds from charges are available, and when they are paid out to an external
        * account. For details, see our [Setting Bank and Debit Card
@@ -2244,8 +3002,12 @@ public static class Payouts {
       String statementDescriptor;
 
       private Payouts(
-          Boolean debitNegativeBalances, Schedule schedule, String statementDescriptor) {
+          Boolean debitNegativeBalances,
+          Map<String, Object> extraParams,
+          Schedule schedule,
+          String statementDescriptor) {
         this.debitNegativeBalances = debitNegativeBalances;
+        this.extraParams = extraParams;
         this.schedule = schedule;
         this.statementDescriptor = statementDescriptor;
       }
@@ -2257,13 +3019,19 @@ public static Builder builder() {
       public static class Builder {
         private Boolean debitNegativeBalances;
 
+        private Map<String, Object> extraParams;
+
         private Schedule schedule;
 
         private String statementDescriptor;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Payouts build() {
-          return new Payouts(this.debitNegativeBalances, this.schedule, this.statementDescriptor);
+          return new Payouts(
+              this.debitNegativeBalances,
+              this.extraParams,
+              this.schedule,
+              this.statementDescriptor);
         }
 
         /**
@@ -2276,6 +3044,34 @@ public Builder setDebitNegativeBalances(Boolean debitNegativeBalances) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Settings.Payouts#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountCreateParams.Settings.Payouts#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * Details on when funds from charges are available, and when they are paid out to an
          * external account. For details, see our [Setting Bank and Debit Card
@@ -2306,6 +3102,16 @@ public static class Schedule {
         @SerializedName("delay_days")
         Object delayDays;
 
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
         /**
          * How frequently available funds are paid out. One of: `daily`, `manual`, `weekly`, or
          * `monthly`. Default is `daily`.
@@ -2328,8 +3134,13 @@ public static class Schedule {
         WeeklyAnchor weeklyAnchor;
 
         private Schedule(
-            Object delayDays, Interval interval, Long monthlyAnchor, WeeklyAnchor weeklyAnchor) {
+            Object delayDays,
+            Map<String, Object> extraParams,
+            Interval interval,
+            Long monthlyAnchor,
+            WeeklyAnchor weeklyAnchor) {
           this.delayDays = delayDays;
+          this.extraParams = extraParams;
           this.interval = interval;
           this.monthlyAnchor = monthlyAnchor;
           this.weeklyAnchor = weeklyAnchor;
@@ -2342,6 +3153,8 @@ public static Builder builder() {
         public static class Builder {
           private Object delayDays;
 
+          private Map<String, Object> extraParams;
+
           private Interval interval;
 
           private Long monthlyAnchor;
@@ -2351,7 +3164,11 @@ public static class Builder {
           /** Finalize and obtain parameter instance from this builder. */
           public Schedule build() {
             return new Schedule(
-                this.delayDays, this.interval, this.monthlyAnchor, this.weeklyAnchor);
+                this.delayDays,
+                this.extraParams,
+                this.interval,
+                this.monthlyAnchor,
+                this.weeklyAnchor);
           }
 
           /**
@@ -2374,6 +3191,34 @@ public Builder setDelayDays(Long delayDays) {
             return this;
           }
 
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountCreateParams.Settings.Payouts.Schedule#extraParams} for the
+           * field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountCreateParams.Settings.Payouts.Schedule#extraParams} for the
+           * field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
+          }
+
           /**
            * How frequently available funds are paid out. One of: `daily`, `manual`, `weekly`, or
            * `monthly`. Default is `daily`.
@@ -2476,6 +3321,15 @@ public static class TosAcceptance {
     @SerializedName("date")
     Long date;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The IP address from which the account representative accepted the Stripe Services Agreement.
      */
@@ -2489,8 +3343,9 @@ public static class TosAcceptance {
     @SerializedName("user_agent")
     String userAgent;
 
-    private TosAcceptance(Long date, String ip, String userAgent) {
+    private TosAcceptance(Long date, Map<String, Object> extraParams, String ip, String userAgent) {
       this.date = date;
+      this.extraParams = extraParams;
       this.ip = ip;
       this.userAgent = userAgent;
     }
@@ -2502,13 +3357,15 @@ public static Builder builder() {
     public static class Builder {
       private Long date;
 
+      private Map<String, Object> extraParams;
+
       private String ip;
 
       private String userAgent;
 
       /** Finalize and obtain parameter instance from this builder. */
       public TosAcceptance build() {
-        return new TosAcceptance(this.date, this.ip, this.userAgent);
+        return new TosAcceptance(this.date, this.extraParams, this.ip, this.userAgent);
       }
 
       /**
@@ -2520,6 +3377,32 @@ public Builder setDate(Long date) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountCreateParams.TosAcceptance#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountCreateParams.TosAcceptance#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * The IP address from which the account representative accepted the Stripe Services
        * Agreement.
@@ -2547,6 +3430,9 @@ public enum RequestedCapability implements ApiRequestParams.EnumParam {
     @SerializedName("card_payments")
     CARD_PAYMENTS("card_payments"),
 
+    @SerializedName("legacy_payments")
+    LEGACY_PAYMENTS("legacy_payments"),
+
     @SerializedName("platform_payments")
     PLATFORM_PAYMENTS("platform_payments");
 
diff --git a/src/main/java/com/stripe/param/AccountLinkCreateParams.java b/src/main/java/com/stripe/param/AccountLinkCreateParams.java
index e65c4918630..84a81ac377e 100644
--- a/src/main/java/com/stripe/param/AccountLinkCreateParams.java
+++ b/src/main/java/com/stripe/param/AccountLinkCreateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class AccountLinkCreateParams extends ApiRequestParams {
@@ -24,6 +26,15 @@ public class AccountLinkCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The URL that the user will be redirected to if the account link is no longer valid. */
   @SerializedName("failure_url")
   String failureUrl;
@@ -43,12 +54,14 @@ private AccountLinkCreateParams(
       String account,
       Collect collect,
       List<String> expand,
+      Map<String, Object> extraParams,
       String failureUrl,
       String successUrl,
       String type) {
     this.account = account;
     this.collect = collect;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.failureUrl = failureUrl;
     this.successUrl = successUrl;
     this.type = type;
@@ -65,6 +78,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String failureUrl;
 
     private String successUrl;
@@ -74,7 +89,13 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public AccountLinkCreateParams build() {
       return new AccountLinkCreateParams(
-          this.account, this.collect, this.expand, this.failureUrl, this.successUrl, this.type);
+          this.account,
+          this.collect,
+          this.expand,
+          this.extraParams,
+          this.failureUrl,
+          this.successUrl,
+          this.type);
     }
 
     /** The identifier of the account to create an account link for. */
@@ -118,6 +139,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AccountLinkCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AccountLinkCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The URL that the user will be redirected to if the account link is no longer valid. */
     public Builder setFailureUrl(String failureUrl) {
       this.failureUrl = failureUrl;
diff --git a/src/main/java/com/stripe/param/AccountListParams.java b/src/main/java/com/stripe/param/AccountListParams.java
index 32b18641fbd..102243c9699 100644
--- a/src/main/java/com/stripe/param/AccountListParams.java
+++ b/src/main/java/com/stripe/param/AccountListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class AccountListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -24,6 +26,15 @@ public class AccountListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -41,10 +52,16 @@ public class AccountListParams extends ApiRequestParams {
   String startingAfter;
 
   private AccountListParams(
-      Object created, String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      Object created,
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -60,6 +77,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -67,7 +86,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public AccountListParams build() {
       return new AccountListParams(
-          this.created, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.created,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     public Builder setCreated(Created created) {
@@ -117,6 +141,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AccountListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AccountListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -139,6 +189,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -155,7 +214,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -167,6 +227,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -177,7 +239,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/AccountPersonsParams.java b/src/main/java/com/stripe/param/AccountPersonsParams.java
index 148c1324a02..abb53789b0e 100644
--- a/src/main/java/com/stripe/param/AccountPersonsParams.java
+++ b/src/main/java/com/stripe/param/AccountPersonsParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class AccountPersonsParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class AccountPersonsParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -47,11 +58,13 @@ public class AccountPersonsParams extends ApiRequestParams {
   private AccountPersonsParams(
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       Relationship relationship,
       String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.relationship = relationship;
     this.startingAfter = startingAfter;
@@ -66,6 +79,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private Relationship relationship;
@@ -75,7 +90,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public AccountPersonsParams build() {
       return new AccountPersonsParams(
-          this.endingBefore, this.expand, this.limit, this.relationship, this.startingAfter);
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.relationship,
+          this.startingAfter);
     }
 
     /**
@@ -115,6 +135,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AccountPersonsParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AccountPersonsParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -160,6 +206,15 @@ public static class Relationship {
     @SerializedName("director")
     Boolean director;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * A filter on the list of people returned based on whether these people are owners of the
      * account's company.
@@ -167,9 +222,11 @@ public static class Relationship {
     @SerializedName("owner")
     Boolean owner;
 
-    private Relationship(Boolean accountOpener, Boolean director, Boolean owner) {
+    private Relationship(
+        Boolean accountOpener, Boolean director, Map<String, Object> extraParams, Boolean owner) {
       this.accountOpener = accountOpener;
       this.director = director;
+      this.extraParams = extraParams;
       this.owner = owner;
     }
 
@@ -182,11 +239,13 @@ public static class Builder {
 
       private Boolean director;
 
+      private Map<String, Object> extraParams;
+
       private Boolean owner;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Relationship build() {
-        return new Relationship(this.accountOpener, this.director, this.owner);
+        return new Relationship(this.accountOpener, this.director, this.extraParams, this.owner);
       }
 
       /**
@@ -207,6 +266,32 @@ public Builder setDirector(Boolean director) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountPersonsParams.Relationship#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountPersonsParams.Relationship#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * A filter on the list of people returned based on whether these people are owners of the
        * account's company.
diff --git a/src/main/java/com/stripe/param/AccountRejectParams.java b/src/main/java/com/stripe/param/AccountRejectParams.java
index cba468835ef..cfbc055b96f 100644
--- a/src/main/java/com/stripe/param/AccountRejectParams.java
+++ b/src/main/java/com/stripe/param/AccountRejectParams.java
@@ -5,19 +5,31 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class AccountRejectParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The reason for rejecting the account. Can be `fraud`, `terms_of_service`, or `other`. */
   @SerializedName("reason")
   String reason;
 
-  private AccountRejectParams(List<String> expand, String reason) {
+  private AccountRejectParams(List<String> expand, Map<String, Object> extraParams, String reason) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.reason = reason;
   }
 
@@ -28,11 +40,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String reason;
 
     /** Finalize and obtain parameter instance from this builder. */
     public AccountRejectParams build() {
-      return new AccountRejectParams(this.expand, this.reason);
+      return new AccountRejectParams(this.expand, this.extraParams, this.reason);
     }
 
     /**
@@ -61,6 +75,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AccountRejectParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AccountRejectParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The reason for rejecting the account. Can be `fraud`, `terms_of_service`, or `other`. */
     public Builder setReason(String reason) {
       this.reason = reason;
diff --git a/src/main/java/com/stripe/param/AccountRetrieveParams.java b/src/main/java/com/stripe/param/AccountRetrieveParams.java
index f7c10089bdc..3be45ded460 100644
--- a/src/main/java/com/stripe/param/AccountRetrieveParams.java
+++ b/src/main/java/com/stripe/param/AccountRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class AccountRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private AccountRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private AccountRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public AccountRetrieveParams build() {
-      return new AccountRetrieveParams(this.expand);
+      return new AccountRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AccountRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AccountRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/AccountUpdateParams.java b/src/main/java/com/stripe/param/AccountUpdateParams.java
index e55d81fdbe9..32a0930264d 100644
--- a/src/main/java/com/stripe/param/AccountUpdateParams.java
+++ b/src/main/java/com/stripe/param/AccountUpdateParams.java
@@ -66,6 +66,15 @@ public class AccountUpdateParams extends ApiRequestParams {
   @SerializedName("external_account")
   String externalAccount;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Information about the person represented by the account. This field is null unless
    * `business_type` is set to `individual`.
@@ -108,6 +117,7 @@ private AccountUpdateParams(
       String email,
       List<String> expand,
       String externalAccount,
+      Map<String, Object> extraParams,
       Individual individual,
       Map<String, String> metadata,
       List<RequestedCapability> requestedCapabilities,
@@ -121,6 +131,7 @@ private AccountUpdateParams(
     this.email = email;
     this.expand = expand;
     this.externalAccount = externalAccount;
+    this.extraParams = extraParams;
     this.individual = individual;
     this.metadata = metadata;
     this.requestedCapabilities = requestedCapabilities;
@@ -149,6 +160,8 @@ public static class Builder {
 
     private String externalAccount;
 
+    private Map<String, Object> extraParams;
+
     private Individual individual;
 
     private Map<String, String> metadata;
@@ -170,6 +183,7 @@ public AccountUpdateParams build() {
           this.email,
           this.expand,
           this.externalAccount,
+          this.extraParams,
           this.individual,
           this.metadata,
           this.requestedCapabilities,
@@ -269,6 +283,32 @@ public Builder setExternalAccount(String externalAccount) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AccountUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AccountUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Information about the person represented by the account. This field is null unless
      * `business_type` is set to `individual`.
@@ -347,6 +387,15 @@ public Builder setTosAcceptance(TosAcceptance tosAcceptance) {
   }
 
   public static class BusinessProfile {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The merchant category code for the account. MCCs are used to classify businesses based on the
      * goods or services they provide.
@@ -382,6 +431,7 @@ public static class BusinessProfile {
     String url;
 
     private BusinessProfile(
+        Map<String, Object> extraParams,
         String mcc,
         String name,
         String productDescription,
@@ -389,6 +439,7 @@ private BusinessProfile(
         String supportPhone,
         String supportUrl,
         String url) {
+      this.extraParams = extraParams;
       this.mcc = mcc;
       this.name = name;
       this.productDescription = productDescription;
@@ -403,6 +454,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String mcc;
 
       private String name;
@@ -420,6 +473,7 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public BusinessProfile build() {
         return new BusinessProfile(
+            this.extraParams,
             this.mcc,
             this.name,
             this.productDescription,
@@ -429,6 +483,32 @@ public BusinessProfile build() {
             this.url);
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountUpdateParams.BusinessProfile#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountUpdateParams.BusinessProfile#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * The merchant category code for the account. MCCs are used to classify businesses based on
        * the goods or services they provide.
@@ -502,6 +582,15 @@ public static class Company {
     @SerializedName("directors_provided")
     Boolean directorsProvided;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The company's legal name. */
     @SerializedName("name")
     String name;
@@ -547,6 +636,7 @@ private Company(
         AddressKana addressKana,
         AddressKanji addressKanji,
         Boolean directorsProvided,
+        Map<String, Object> extraParams,
         String name,
         String nameKana,
         String nameKanji,
@@ -559,6 +649,7 @@ private Company(
       this.addressKana = addressKana;
       this.addressKanji = addressKanji;
       this.directorsProvided = directorsProvided;
+      this.extraParams = extraParams;
       this.name = name;
       this.nameKana = nameKana;
       this.nameKanji = nameKanji;
@@ -582,6 +673,8 @@ public static class Builder {
 
       private Boolean directorsProvided;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String nameKana;
@@ -605,6 +698,7 @@ public Company build() {
             this.addressKana,
             this.addressKanji,
             this.directorsProvided,
+            this.extraParams,
             this.name,
             this.nameKana,
             this.nameKanji,
@@ -645,6 +739,32 @@ public Builder setDirectorsProvided(Boolean directorsProvided) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountUpdateParams.Company#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountUpdateParams.Company#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The company's legal name. */
       public Builder setName(String name) {
         this.name = name;
@@ -714,6 +834,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Address line 1 (e.g., street, PO Box, or company name). */
       @SerializedName("line1")
       String line1;
@@ -733,12 +862,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -754,6 +885,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -765,7 +898,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         /** City, district, suburb, town, or village. */
@@ -783,6 +922,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Company.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Company.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Address line 1 (e.g., street, PO Box, or company name). */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -821,6 +988,15 @@ public static class AddressKana {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Block or building number. */
       @SerializedName("line1")
       String line1;
@@ -844,6 +1020,7 @@ public static class AddressKana {
       private AddressKana(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
@@ -851,6 +1028,7 @@ private AddressKana(
           String town) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -867,6 +1045,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -882,6 +1062,7 @@ public AddressKana build() {
           return new AddressKana(
               this.city,
               this.country,
+              this.extraParams,
               this.line1,
               this.line2,
               this.postalCode,
@@ -904,6 +1085,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Company.AddressKana#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Company.AddressKana#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Block or building number. */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -948,6 +1157,15 @@ public static class AddressKanji {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Block or building number. */
       @SerializedName("line1")
       String line1;
@@ -971,6 +1189,7 @@ public static class AddressKanji {
       private AddressKanji(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
@@ -978,6 +1197,7 @@ private AddressKanji(
           String town) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -994,6 +1214,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -1009,6 +1231,7 @@ public AddressKanji build() {
           return new AddressKanji(
               this.city,
               this.country,
+              this.extraParams,
               this.line1,
               this.line2,
               this.postalCode,
@@ -1031,6 +1254,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Company.AddressKanji#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Company.AddressKanji#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Block or building number. */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -1084,6 +1335,15 @@ public static class Individual {
     @SerializedName("email")
     String email;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The individual's first name. */
     @SerializedName("first_name")
     String firstName;
@@ -1152,6 +1412,7 @@ private Individual(
         AddressKanji addressKanji,
         Dob dob,
         String email,
+        Map<String, Object> extraParams,
         String firstName,
         String firstNameKana,
         String firstNameKanji,
@@ -1170,6 +1431,7 @@ private Individual(
       this.addressKanji = addressKanji;
       this.dob = dob;
       this.email = email;
+      this.extraParams = extraParams;
       this.firstName = firstName;
       this.firstNameKana = firstNameKana;
       this.firstNameKanji = firstNameKanji;
@@ -1200,6 +1462,8 @@ public static class Builder {
 
       private String email;
 
+      private Map<String, Object> extraParams;
+
       private String firstName;
 
       private String firstNameKana;
@@ -1234,6 +1498,7 @@ public Individual build() {
             this.addressKanji,
             this.dob,
             this.email,
+            this.extraParams,
             this.firstName,
             this.firstNameKana,
             this.firstNameKanji,
@@ -1278,6 +1543,32 @@ public Builder setEmail(String email) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountUpdateParams.Individual#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountUpdateParams.Individual#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The individual's first name. */
       public Builder setFirstName(String firstName) {
         this.firstName = firstName;
@@ -1394,6 +1685,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Address line 1 (e.g., street, PO Box, or company name). */
       @SerializedName("line1")
       String line1;
@@ -1413,12 +1713,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -1434,6 +1736,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -1445,7 +1749,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         /** City, district, suburb, town, or village. */
@@ -1463,6 +1773,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Address line 1 (e.g., street, PO Box, or company name). */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -1501,6 +1839,15 @@ public static class AddressKana {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Block or building number. */
       @SerializedName("line1")
       String line1;
@@ -1524,6 +1871,7 @@ public static class AddressKana {
       private AddressKana(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
@@ -1531,6 +1879,7 @@ private AddressKana(
           String town) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -1547,6 +1896,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -1562,6 +1913,7 @@ public AddressKana build() {
           return new AddressKana(
               this.city,
               this.country,
+              this.extraParams,
               this.line1,
               this.line2,
               this.postalCode,
@@ -1584,6 +1936,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.AddressKana#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.AddressKana#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Block or building number. */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -1628,6 +2008,15 @@ public static class AddressKanji {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Block or building number. */
       @SerializedName("line1")
       String line1;
@@ -1651,6 +2040,7 @@ public static class AddressKanji {
       private AddressKanji(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
@@ -1658,6 +2048,7 @@ private AddressKanji(
           String town) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -1674,6 +2065,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -1689,6 +2082,7 @@ public AddressKanji build() {
           return new AddressKanji(
               this.city,
               this.country,
+              this.extraParams,
               this.line1,
               this.line2,
               this.postalCode,
@@ -1711,6 +2105,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.AddressKanji#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.AddressKanji#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Block or building number. */
         public Builder setLine1(String line1) {
           this.line1 = line1;
@@ -1748,6 +2170,15 @@ public static class Dob {
       @SerializedName("day")
       Long day;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** The month of birth, between 1 and 12. */
       @SerializedName("month")
       Long month;
@@ -1756,8 +2187,9 @@ public static class Dob {
       @SerializedName("year")
       Long year;
 
-      private Dob(Long day, Long month, Long year) {
+      private Dob(Long day, Map<String, Object> extraParams, Long month, Long year) {
         this.day = day;
+        this.extraParams = extraParams;
         this.month = month;
         this.year = year;
       }
@@ -1769,13 +2201,15 @@ public static Builder builder() {
       public static class Builder {
         private Long day;
 
+        private Map<String, Object> extraParams;
+
         private Long month;
 
         private Long year;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Dob build() {
-          return new Dob(this.day, this.month, this.year);
+          return new Dob(this.day, this.extraParams, this.month, this.year);
         }
 
         /** The day of birth, between 1 and 31. */
@@ -1784,6 +2218,34 @@ public Builder setDay(Long day) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.Dob#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.Dob#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** The month of birth, between 1 and 12. */
         public Builder setMonth(Long month) {
           this.month = month;
@@ -1803,8 +2265,18 @@ public static class Verification {
       @SerializedName("document")
       Document document;
 
-      private Verification(Document document) {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
+      private Verification(Document document, Map<String, Object> extraParams) {
         this.document = document;
+        this.extraParams = extraParams;
       }
 
       public static Builder builder() {
@@ -1814,9 +2286,11 @@ public static Builder builder() {
       public static class Builder {
         private Document document;
 
+        private Map<String, Object> extraParams;
+
         /** Finalize and obtain parameter instance from this builder. */
         public Verification build() {
-          return new Verification(this.document);
+          return new Verification(this.document, this.extraParams);
         }
 
         /** An identifying document, either a passport or local ID card. */
@@ -1824,6 +2298,34 @@ public Builder setDocument(Document document) {
           this.document = document;
           return this;
         }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.Verification#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Individual.Verification#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
       }
 
       public static class Document {
@@ -1834,6 +2336,16 @@ public static class Document {
         @SerializedName("back")
         String back;
 
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
         /**
          * The front of an ID returned by a [file upload](#create_file) with a `purpose` value of
          * `identity_document`.
@@ -1841,8 +2353,9 @@ public static class Document {
         @SerializedName("front")
         String front;
 
-        private Document(String back, String front) {
+        private Document(String back, Map<String, Object> extraParams, String front) {
           this.back = back;
+          this.extraParams = extraParams;
           this.front = front;
         }
 
@@ -1854,11 +2367,13 @@ public static Builder builder() {
         public static class Builder {
           private String back;
 
+          private Map<String, Object> extraParams;
+
           private String front;
 
           /** Finalize and obtain parameter instance from this builder. */
           public Document build() {
-            return new Document(this.back, this.front);
+            return new Document(this.back, this.extraParams, this.front);
           }
 
           /**
@@ -1870,6 +2385,34 @@ public Builder setBack(String back) {
             return this;
           }
 
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountUpdateParams.Individual.Verification.Document#extraParams} for
+           * the field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountUpdateParams.Individual.Verification.Document#extraParams} for
+           * the field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
+          }
+
           /**
            * The front of an ID returned by a [file upload](#create_file) with a `purpose` value of
            * `identity_document`.
@@ -1895,6 +2438,15 @@ public static class Settings {
     @SerializedName("card_payments")
     CardPayments cardPayments;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Settings that apply across payment methods for charging on the account. */
     @SerializedName("payments")
     Payments payments;
@@ -1904,9 +2456,14 @@ public static class Settings {
     Payouts payouts;
 
     private Settings(
-        Branding branding, CardPayments cardPayments, Payments payments, Payouts payouts) {
+        Branding branding,
+        CardPayments cardPayments,
+        Map<String, Object> extraParams,
+        Payments payments,
+        Payouts payouts) {
       this.branding = branding;
       this.cardPayments = cardPayments;
+      this.extraParams = extraParams;
       this.payments = payments;
       this.payouts = payouts;
     }
@@ -1920,13 +2477,16 @@ public static class Builder {
 
       private CardPayments cardPayments;
 
+      private Map<String, Object> extraParams;
+
       private Payments payments;
 
       private Payouts payouts;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Settings build() {
-        return new Settings(this.branding, this.cardPayments, this.payments, this.payouts);
+        return new Settings(
+            this.branding, this.cardPayments, this.extraParams, this.payments, this.payouts);
       }
 
       /**
@@ -1944,6 +2504,32 @@ public Builder setCardPayments(CardPayments cardPayments) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountUpdateParams.Settings#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountUpdateParams.Settings#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Settings that apply across payment methods for charging on the account. */
       public Builder setPayments(Payments payments) {
         this.payments = payments;
@@ -1958,6 +2544,15 @@ public Builder setPayouts(Payouts payouts) {
     }
 
     public static class Branding {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * (ID of a [file upload](https://stripe.com/docs/guides/file-upload)) An icon for the
        * account. Must be square and at least 128px x 128px.
@@ -1977,7 +2572,9 @@ public static class Branding {
       @SerializedName("primary_color")
       String primaryColor;
 
-      private Branding(String icon, String logo, String primaryColor) {
+      private Branding(
+          Map<String, Object> extraParams, String icon, String logo, String primaryColor) {
+        this.extraParams = extraParams;
         this.icon = icon;
         this.logo = logo;
         this.primaryColor = primaryColor;
@@ -1988,6 +2585,8 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private String icon;
 
         private String logo;
@@ -1996,7 +2595,35 @@ public static class Builder {
 
         /** Finalize and obtain parameter instance from this builder. */
         public Branding build() {
-          return new Branding(this.icon, this.logo, this.primaryColor);
+          return new Branding(this.extraParams, this.icon, this.logo, this.primaryColor);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Settings.Branding#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Settings.Branding#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /**
@@ -2034,6 +2661,15 @@ public static class CardPayments {
       @SerializedName("decline_on")
       DeclineOn declineOn;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The default text that appears on credit card statements when a charge is made. This field
        * prefixes any dynamic `statement_descriptor` specified on the charge.
@@ -2043,8 +2679,10 @@ public static class CardPayments {
       @SerializedName("statement_descriptor_prefix")
       String statementDescriptorPrefix;
 
-      private CardPayments(DeclineOn declineOn, String statementDescriptorPrefix) {
+      private CardPayments(
+          DeclineOn declineOn, Map<String, Object> extraParams, String statementDescriptorPrefix) {
         this.declineOn = declineOn;
+        this.extraParams = extraParams;
         this.statementDescriptorPrefix = statementDescriptorPrefix;
       }
 
@@ -2055,11 +2693,13 @@ public static Builder builder() {
       public static class Builder {
         private DeclineOn declineOn;
 
+        private Map<String, Object> extraParams;
+
         private String statementDescriptorPrefix;
 
         /** Finalize and obtain parameter instance from this builder. */
         public CardPayments build() {
-          return new CardPayments(this.declineOn, this.statementDescriptorPrefix);
+          return new CardPayments(this.declineOn, this.extraParams, this.statementDescriptorPrefix);
         }
 
         /**
@@ -2071,6 +2711,34 @@ public Builder setDeclineOn(DeclineOn declineOn) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Settings.CardPayments#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Settings.CardPayments#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * The default text that appears on credit card statements when a charge is made. This field
          * prefixes any dynamic `statement_descriptor` specified on the charge.
@@ -2099,9 +2767,20 @@ public static class DeclineOn {
         @SerializedName("cvc_failure")
         Boolean cvcFailure;
 
-        private DeclineOn(Boolean avsFailure, Boolean cvcFailure) {
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
+        private DeclineOn(Boolean avsFailure, Boolean cvcFailure, Map<String, Object> extraParams) {
           this.avsFailure = avsFailure;
           this.cvcFailure = cvcFailure;
+          this.extraParams = extraParams;
         }
 
         public static Builder builder() {
@@ -2113,9 +2792,11 @@ public static class Builder {
 
           private Boolean cvcFailure;
 
+          private Map<String, Object> extraParams;
+
           /** Finalize and obtain parameter instance from this builder. */
           public DeclineOn build() {
-            return new DeclineOn(this.avsFailure, this.cvcFailure);
+            return new DeclineOn(this.avsFailure, this.cvcFailure, this.extraParams);
           }
 
           /**
@@ -2136,11 +2817,48 @@ public Builder setCvcFailure(Boolean cvcFailure) {
             this.cvcFailure = cvcFailure;
             return this;
           }
+
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountUpdateParams.Settings.CardPayments.DeclineOn#extraParams} for
+           * the field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountUpdateParams.Settings.CardPayments.DeclineOn#extraParams} for
+           * the field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
+          }
         }
       }
     }
 
     public static class Payments {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The default text that appears on credit card statements when a charge is made. This field
        * prefixes any dynamic `statement_descriptor` specified on the charge.
@@ -2148,7 +2866,8 @@ public static class Payments {
       @SerializedName("statement_descriptor")
       String statementDescriptor;
 
-      private Payments(String statementDescriptor) {
+      private Payments(Map<String, Object> extraParams, String statementDescriptor) {
+        this.extraParams = extraParams;
         this.statementDescriptor = statementDescriptor;
       }
 
@@ -2157,11 +2876,41 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private String statementDescriptor;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Payments build() {
-          return new Payments(this.statementDescriptor);
+          return new Payments(this.extraParams, this.statementDescriptor);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Settings.Payments#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Settings.Payments#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /**
@@ -2184,6 +2933,15 @@ public static class Payouts {
       @SerializedName("debit_negative_balances")
       Boolean debitNegativeBalances;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * Details on when funds from charges are available, and when they are paid out to an external
        * account. For details, see our [Setting Bank and Debit Card
@@ -2200,8 +2958,12 @@ public static class Payouts {
       String statementDescriptor;
 
       private Payouts(
-          Boolean debitNegativeBalances, Schedule schedule, String statementDescriptor) {
+          Boolean debitNegativeBalances,
+          Map<String, Object> extraParams,
+          Schedule schedule,
+          String statementDescriptor) {
         this.debitNegativeBalances = debitNegativeBalances;
+        this.extraParams = extraParams;
         this.schedule = schedule;
         this.statementDescriptor = statementDescriptor;
       }
@@ -2213,13 +2975,19 @@ public static Builder builder() {
       public static class Builder {
         private Boolean debitNegativeBalances;
 
+        private Map<String, Object> extraParams;
+
         private Schedule schedule;
 
         private String statementDescriptor;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Payouts build() {
-          return new Payouts(this.debitNegativeBalances, this.schedule, this.statementDescriptor);
+          return new Payouts(
+              this.debitNegativeBalances,
+              this.extraParams,
+              this.schedule,
+              this.statementDescriptor);
         }
 
         /**
@@ -2232,6 +3000,34 @@ public Builder setDebitNegativeBalances(Boolean debitNegativeBalances) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Settings.Payouts#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link AccountUpdateParams.Settings.Payouts#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * Details on when funds from charges are available, and when they are paid out to an
          * external account. For details, see our [Setting Bank and Debit Card
@@ -2262,6 +3058,16 @@ public static class Schedule {
         @SerializedName("delay_days")
         Object delayDays;
 
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
         /**
          * How frequently available funds are paid out. One of: `daily`, `manual`, `weekly`, or
          * `monthly`. Default is `daily`.
@@ -2284,8 +3090,13 @@ public static class Schedule {
         WeeklyAnchor weeklyAnchor;
 
         private Schedule(
-            Object delayDays, Interval interval, Long monthlyAnchor, WeeklyAnchor weeklyAnchor) {
+            Object delayDays,
+            Map<String, Object> extraParams,
+            Interval interval,
+            Long monthlyAnchor,
+            WeeklyAnchor weeklyAnchor) {
           this.delayDays = delayDays;
+          this.extraParams = extraParams;
           this.interval = interval;
           this.monthlyAnchor = monthlyAnchor;
           this.weeklyAnchor = weeklyAnchor;
@@ -2298,6 +3109,8 @@ public static Builder builder() {
         public static class Builder {
           private Object delayDays;
 
+          private Map<String, Object> extraParams;
+
           private Interval interval;
 
           private Long monthlyAnchor;
@@ -2307,7 +3120,11 @@ public static class Builder {
           /** Finalize and obtain parameter instance from this builder. */
           public Schedule build() {
             return new Schedule(
-                this.delayDays, this.interval, this.monthlyAnchor, this.weeklyAnchor);
+                this.delayDays,
+                this.extraParams,
+                this.interval,
+                this.monthlyAnchor,
+                this.weeklyAnchor);
           }
 
           /**
@@ -2330,6 +3147,34 @@ public Builder setDelayDays(Long delayDays) {
             return this;
           }
 
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountUpdateParams.Settings.Payouts.Schedule#extraParams} for the
+           * field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link AccountUpdateParams.Settings.Payouts.Schedule#extraParams} for the
+           * field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
+          }
+
           /**
            * How frequently available funds are paid out. One of: `daily`, `manual`, `weekly`, or
            * `monthly`. Default is `daily`.
@@ -2432,6 +3277,15 @@ public static class TosAcceptance {
     @SerializedName("date")
     Long date;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The IP address from which the account representative accepted the Stripe Services Agreement.
      */
@@ -2445,8 +3299,9 @@ public static class TosAcceptance {
     @SerializedName("user_agent")
     String userAgent;
 
-    private TosAcceptance(Long date, String ip, String userAgent) {
+    private TosAcceptance(Long date, Map<String, Object> extraParams, String ip, String userAgent) {
       this.date = date;
+      this.extraParams = extraParams;
       this.ip = ip;
       this.userAgent = userAgent;
     }
@@ -2458,13 +3313,15 @@ public static Builder builder() {
     public static class Builder {
       private Long date;
 
+      private Map<String, Object> extraParams;
+
       private String ip;
 
       private String userAgent;
 
       /** Finalize and obtain parameter instance from this builder. */
       public TosAcceptance build() {
-        return new TosAcceptance(this.date, this.ip, this.userAgent);
+        return new TosAcceptance(this.date, this.extraParams, this.ip, this.userAgent);
       }
 
       /**
@@ -2476,6 +3333,32 @@ public Builder setDate(Long date) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AccountUpdateParams.TosAcceptance#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AccountUpdateParams.TosAcceptance#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * The IP address from which the account representative accepted the Stripe Services
        * Agreement.
@@ -2503,6 +3386,9 @@ public enum RequestedCapability implements ApiRequestParams.EnumParam {
     @SerializedName("card_payments")
     CARD_PAYMENTS("card_payments"),
 
+    @SerializedName("legacy_payments")
+    LEGACY_PAYMENTS("legacy_payments"),
+
     @SerializedName("platform_payments")
     PLATFORM_PAYMENTS("platform_payments");
 
diff --git a/src/main/java/com/stripe/param/ApplePayDomainCreateParams.java b/src/main/java/com/stripe/param/ApplePayDomainCreateParams.java
index 3b3e794df91..d8cfa9a146b 100644
--- a/src/main/java/com/stripe/param/ApplePayDomainCreateParams.java
+++ b/src/main/java/com/stripe/param/ApplePayDomainCreateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ApplePayDomainCreateParams extends ApiRequestParams {
   @SerializedName("domain_name")
@@ -15,9 +17,20 @@ public class ApplePayDomainCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
-  private ApplePayDomainCreateParams(String domainName, List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ApplePayDomainCreateParams(
+      String domainName, List<String> expand, Map<String, Object> extraParams) {
     this.domainName = domainName;
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -29,9 +42,11 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ApplePayDomainCreateParams build() {
-      return new ApplePayDomainCreateParams(this.domainName, this.expand);
+      return new ApplePayDomainCreateParams(this.domainName, this.expand, this.extraParams);
     }
 
     public Builder setDomainName(String domainName) {
@@ -64,5 +79,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ApplePayDomainCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ApplePayDomainCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/ApplePayDomainListParams.java b/src/main/java/com/stripe/param/ApplePayDomainListParams.java
index bb0cf94d47f..48a7588ffa7 100644
--- a/src/main/java/com/stripe/param/ApplePayDomainListParams.java
+++ b/src/main/java/com/stripe/param/ApplePayDomainListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ApplePayDomainListParams extends ApiRequestParams {
   @SerializedName("domain_name")
@@ -24,6 +26,15 @@ public class ApplePayDomainListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -44,11 +55,13 @@ private ApplePayDomainListParams(
       String domainName,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter) {
     this.domainName = domainName;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -64,6 +77,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -71,7 +86,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public ApplePayDomainListParams build() {
       return new ApplePayDomainListParams(
-          this.domainName, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.domainName,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     public Builder setDomainName(String domainName) {
@@ -116,6 +136,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ApplePayDomainListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ApplePayDomainListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/ApplePayDomainRetrieveParams.java b/src/main/java/com/stripe/param/ApplePayDomainRetrieveParams.java
index 789b68f1880..2051f923999 100644
--- a/src/main/java/com/stripe/param/ApplePayDomainRetrieveParams.java
+++ b/src/main/java/com/stripe/param/ApplePayDomainRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ApplePayDomainRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ApplePayDomainRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ApplePayDomainRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ApplePayDomainRetrieveParams build() {
-      return new ApplePayDomainRetrieveParams(this.expand);
+      return new ApplePayDomainRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ApplePayDomainRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ApplePayDomainRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/ApplicationFeeListParams.java b/src/main/java/com/stripe/param/ApplicationFeeListParams.java
index c0f79716f54..d997ce60e1d 100644
--- a/src/main/java/com/stripe/param/ApplicationFeeListParams.java
+++ b/src/main/java/com/stripe/param/ApplicationFeeListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ApplicationFeeListParams extends ApiRequestParams {
   /** Only return application fees for the charge specified by this charge ID. */
@@ -28,6 +30,15 @@ public class ApplicationFeeListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -49,12 +60,14 @@ private ApplicationFeeListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter) {
     this.charge = charge;
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -72,6 +85,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -83,6 +98,7 @@ public ApplicationFeeListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter);
     }
@@ -140,6 +156,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ApplicationFeeListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ApplicationFeeListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -162,6 +204,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -178,7 +229,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -190,6 +242,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -200,7 +254,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ApplicationFeeListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ApplicationFeeListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/ApplicationFeeRetrieveParams.java b/src/main/java/com/stripe/param/ApplicationFeeRetrieveParams.java
index e55b87320de..126e3ff8797 100644
--- a/src/main/java/com/stripe/param/ApplicationFeeRetrieveParams.java
+++ b/src/main/java/com/stripe/param/ApplicationFeeRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ApplicationFeeRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ApplicationFeeRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ApplicationFeeRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ApplicationFeeRetrieveParams build() {
-      return new ApplicationFeeRetrieveParams(this.expand);
+      return new ApplicationFeeRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ApplicationFeeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ApplicationFeeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/BalanceRetrieveParams.java b/src/main/java/com/stripe/param/BalanceRetrieveParams.java
index 04bed51d2c9..073020028e8 100644
--- a/src/main/java/com/stripe/param/BalanceRetrieveParams.java
+++ b/src/main/java/com/stripe/param/BalanceRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class BalanceRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private BalanceRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private BalanceRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public BalanceRetrieveParams build() {
-      return new BalanceRetrieveParams(this.expand);
+      return new BalanceRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BalanceRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BalanceRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/BalanceTransactionListParams.java b/src/main/java/com/stripe/param/BalanceTransactionListParams.java
index b4a34be6bf1..33540425273 100644
--- a/src/main/java/com/stripe/param/BalanceTransactionListParams.java
+++ b/src/main/java/com/stripe/param/BalanceTransactionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class BalanceTransactionListParams extends ApiRequestParams {
   @SerializedName("available_on")
@@ -30,6 +32,15 @@ public class BalanceTransactionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -71,6 +82,7 @@ private BalanceTransactionListParams(
       String currency,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String payout,
       String source,
@@ -81,6 +93,7 @@ private BalanceTransactionListParams(
     this.currency = currency;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.payout = payout;
     this.source = source;
@@ -103,6 +116,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String payout;
@@ -121,6 +136,7 @@ public BalanceTransactionListParams build() {
           this.currency,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.payout,
           this.source,
@@ -190,6 +206,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BalanceTransactionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BalanceTransactionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -237,6 +279,15 @@ public Builder setType(String type) {
   }
 
   public static class AvailableOn {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -253,7 +304,8 @@ public static class AvailableOn {
     @SerializedName("lte")
     Long lte;
 
-    private AvailableOn(Long gt, Long gte, Long lt, Long lte) {
+    private AvailableOn(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -265,6 +317,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -275,7 +329,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public AvailableOn build() {
-        return new AvailableOn(this.gt, this.gte, this.lt, this.lte);
+        return new AvailableOn(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * BalanceTransactionListParams.AvailableOn#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link BalanceTransactionListParams.AvailableOn#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -305,6 +386,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -321,7 +411,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -333,6 +424,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -343,7 +436,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * BalanceTransactionListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link BalanceTransactionListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/BalanceTransactionRetrieveParams.java b/src/main/java/com/stripe/param/BalanceTransactionRetrieveParams.java
index 0af98c3c15b..58682d5a98e 100644
--- a/src/main/java/com/stripe/param/BalanceTransactionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/BalanceTransactionRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class BalanceTransactionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private BalanceTransactionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private BalanceTransactionRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public BalanceTransactionRetrieveParams build() {
-      return new BalanceTransactionRetrieveParams(this.expand);
+      return new BalanceTransactionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BalanceTransactionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BalanceTransactionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/BankAccountUpdateOnAccountParams.java b/src/main/java/com/stripe/param/BankAccountUpdateOnAccountParams.java
index 73e4b804f44..9f3d035261d 100644
--- a/src/main/java/com/stripe/param/BankAccountUpdateOnAccountParams.java
+++ b/src/main/java/com/stripe/param/BankAccountUpdateOnAccountParams.java
@@ -28,6 +28,15 @@ public class BankAccountUpdateOnAccountParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
@@ -36,11 +45,13 @@ private BankAccountUpdateOnAccountParams(
       ApiRequestParams.EnumParam accountHolderType,
       Boolean defaultForCurrency,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata) {
     this.accountHolderName = accountHolderName;
     this.accountHolderType = accountHolderType;
     this.defaultForCurrency = defaultForCurrency;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -57,6 +68,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
@@ -66,6 +79,7 @@ public BankAccountUpdateOnAccountParams build() {
           this.accountHolderType,
           this.defaultForCurrency,
           this.expand,
+          this.extraParams,
           this.metadata);
     }
 
@@ -119,6 +133,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BankAccountUpdateOnAccountParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BankAccountUpdateOnAccountParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/BankAccountUpdateOnCustomerParams.java b/src/main/java/com/stripe/param/BankAccountUpdateOnCustomerParams.java
index 3700aaaa354..c80bb79f8ad 100644
--- a/src/main/java/com/stripe/param/BankAccountUpdateOnCustomerParams.java
+++ b/src/main/java/com/stripe/param/BankAccountUpdateOnCustomerParams.java
@@ -23,6 +23,15 @@ public class BankAccountUpdateOnCustomerParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
@@ -30,10 +39,12 @@ private BankAccountUpdateOnCustomerParams(
       String accountHolderName,
       AccountHolderType accountHolderType,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata) {
     this.accountHolderName = accountHolderName;
     this.accountHolderType = accountHolderType;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -48,12 +59,18 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public BankAccountUpdateOnCustomerParams build() {
       return new BankAccountUpdateOnCustomerParams(
-          this.accountHolderName, this.accountHolderType, this.expand, this.metadata);
+          this.accountHolderName,
+          this.accountHolderType,
+          this.expand,
+          this.extraParams,
+          this.metadata);
     }
 
     /** The name of the person or business that owns the bank account. */
@@ -94,6 +111,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BankAccountUpdateOnCustomerParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BankAccountUpdateOnCustomerParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/BankAccountVerifyParams.java b/src/main/java/com/stripe/param/BankAccountVerifyParams.java
index 949b3c8719a..fab6e7b7602 100644
--- a/src/main/java/com/stripe/param/BankAccountVerifyParams.java
+++ b/src/main/java/com/stripe/param/BankAccountVerifyParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class BankAccountVerifyParams extends ApiRequestParams {
   /**
@@ -19,9 +21,20 @@ public class BankAccountVerifyParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
-  private BankAccountVerifyParams(List<Long> amounts, List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private BankAccountVerifyParams(
+      List<Long> amounts, List<String> expand, Map<String, Object> extraParams) {
     this.amounts = amounts;
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -33,9 +46,11 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public BankAccountVerifyParams build() {
-      return new BankAccountVerifyParams(this.amounts, this.expand);
+      return new BankAccountVerifyParams(this.amounts, this.expand, this.extraParams);
     }
 
     /**
@@ -89,5 +104,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BankAccountVerifyParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BankAccountVerifyParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/BitcoinReceiverListParams.java b/src/main/java/com/stripe/param/BitcoinReceiverListParams.java
index 8198a27516a..6030bf175b0 100644
--- a/src/main/java/com/stripe/param/BitcoinReceiverListParams.java
+++ b/src/main/java/com/stripe/param/BitcoinReceiverListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class BitcoinReceiverListParams extends ApiRequestParams {
   /** Filter for active receivers. */
@@ -25,6 +27,15 @@ public class BitcoinReceiverListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Filter for filled receivers. */
   @SerializedName("filled")
   Boolean filled;
@@ -53,6 +64,7 @@ private BitcoinReceiverListParams(
       Boolean active,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Boolean filled,
       Long limit,
       String startingAfter,
@@ -60,6 +72,7 @@ private BitcoinReceiverListParams(
     this.active = active;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.filled = filled;
     this.limit = limit;
     this.startingAfter = startingAfter;
@@ -77,6 +90,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean filled;
 
     private Long limit;
@@ -91,6 +106,7 @@ public BitcoinReceiverListParams build() {
           this.active,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.filled,
           this.limit,
           this.startingAfter,
@@ -140,6 +156,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BitcoinReceiverListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BitcoinReceiverListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Filter for filled receivers. */
     public Builder setFilled(Boolean filled) {
       this.filled = filled;
diff --git a/src/main/java/com/stripe/param/BitcoinReceiverRetrieveParams.java b/src/main/java/com/stripe/param/BitcoinReceiverRetrieveParams.java
index d32927958d6..f0013e71d41 100644
--- a/src/main/java/com/stripe/param/BitcoinReceiverRetrieveParams.java
+++ b/src/main/java/com/stripe/param/BitcoinReceiverRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class BitcoinReceiverRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private BitcoinReceiverRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private BitcoinReceiverRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public BitcoinReceiverRetrieveParams build() {
-      return new BitcoinReceiverRetrieveParams(this.expand);
+      return new BitcoinReceiverRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BitcoinReceiverRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BitcoinReceiverRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/BitcoinTransactionCollectionListParams.java b/src/main/java/com/stripe/param/BitcoinTransactionCollectionListParams.java
index 049942d7e76..bc3ca67c147 100644
--- a/src/main/java/com/stripe/param/BitcoinTransactionCollectionListParams.java
+++ b/src/main/java/com/stripe/param/BitcoinTransactionCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class BitcoinTransactionCollectionListParams extends ApiRequestParams {
   /** Only return transactions for the customer specified by this customer ID. */
@@ -25,6 +27,15 @@ public class BitcoinTransactionCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -42,10 +53,16 @@ public class BitcoinTransactionCollectionListParams extends ApiRequestParams {
   String startingAfter;
 
   private BitcoinTransactionCollectionListParams(
-      String customer, String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String customer,
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.customer = customer;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -61,6 +78,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -68,7 +87,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public BitcoinTransactionCollectionListParams build() {
       return new BitcoinTransactionCollectionListParams(
-          this.customer, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.customer,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     /** Only return transactions for the customer specified by this customer ID. */
@@ -114,6 +138,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * BitcoinTransactionCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link BitcoinTransactionCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/CardUpdateOnAccountParams.java b/src/main/java/com/stripe/param/CardUpdateOnAccountParams.java
index 8054816fa59..d7d85201439 100644
--- a/src/main/java/com/stripe/param/CardUpdateOnAccountParams.java
+++ b/src/main/java/com/stripe/param/CardUpdateOnAccountParams.java
@@ -50,6 +50,15 @@ public class CardUpdateOnAccountParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
@@ -68,6 +77,7 @@ private CardUpdateOnAccountParams(
       String expMonth,
       String expYear,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String name) {
     this.addressCity = addressCity;
@@ -80,6 +90,7 @@ private CardUpdateOnAccountParams(
     this.expMonth = expMonth;
     this.expYear = expYear;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.name = name;
   }
@@ -109,6 +120,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String name;
@@ -126,6 +139,7 @@ public CardUpdateOnAccountParams build() {
           this.expMonth,
           this.expYear,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.name);
     }
@@ -210,6 +224,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardUpdateOnAccountParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardUpdateOnAccountParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/CardUpdateOnCustomerParams.java b/src/main/java/com/stripe/param/CardUpdateOnCustomerParams.java
index eebb369bd53..3b70c6fd364 100644
--- a/src/main/java/com/stripe/param/CardUpdateOnCustomerParams.java
+++ b/src/main/java/com/stripe/param/CardUpdateOnCustomerParams.java
@@ -46,6 +46,15 @@ public class CardUpdateOnCustomerParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
@@ -63,6 +72,7 @@ private CardUpdateOnCustomerParams(
       String expMonth,
       String expYear,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String name) {
     this.addressCity = addressCity;
@@ -74,6 +84,7 @@ private CardUpdateOnCustomerParams(
     this.expMonth = expMonth;
     this.expYear = expYear;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.name = name;
   }
@@ -101,6 +112,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String name;
@@ -117,6 +130,7 @@ public CardUpdateOnCustomerParams build() {
           this.expMonth,
           this.expYear,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.name);
     }
@@ -195,6 +209,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardUpdateOnCustomerParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardUpdateOnCustomerParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/ChargeCaptureParams.java b/src/main/java/com/stripe/param/ChargeCaptureParams.java
index 301c9d9c5c2..1019d122b3e 100644
--- a/src/main/java/com/stripe/param/ChargeCaptureParams.java
+++ b/src/main/java/com/stripe/param/ChargeCaptureParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ChargeCaptureParams extends ApiRequestParams {
   /**
@@ -30,6 +32,15 @@ public class ChargeCaptureParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * The email address to send this charge's receipt to. This will override the previously-specified
    * email address for this charge, if one was set. Receipts will not be sent in test mode.
@@ -75,6 +86,7 @@ private ChargeCaptureParams(
       Long applicationFee,
       Long applicationFeeAmount,
       List<String> expand,
+      Map<String, Object> extraParams,
       String receiptEmail,
       String statementDescriptor,
       TransferData transferData,
@@ -83,6 +95,7 @@ private ChargeCaptureParams(
     this.applicationFee = applicationFee;
     this.applicationFeeAmount = applicationFeeAmount;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.receiptEmail = receiptEmail;
     this.statementDescriptor = statementDescriptor;
     this.transferData = transferData;
@@ -102,6 +115,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String receiptEmail;
 
     private String statementDescriptor;
@@ -117,6 +132,7 @@ public ChargeCaptureParams build() {
           this.applicationFee,
           this.applicationFeeAmount,
           this.expand,
+          this.extraParams,
           this.receiptEmail,
           this.statementDescriptor,
           this.transferData,
@@ -173,6 +189,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ChargeCaptureParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ChargeCaptureParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * The email address to send this charge's receipt to. This will override the
      * previously-specified email address for this charge, if one was set. Receipts will not be sent
@@ -231,8 +273,18 @@ public static class TransferData {
     @SerializedName("amount")
     Long amount;
 
-    private TransferData(Long amount) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private TransferData(Long amount, Map<String, Object> extraParams) {
       this.amount = amount;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -242,9 +294,11 @@ public static Builder builder() {
     public static class Builder {
       private Long amount;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public TransferData build() {
-        return new TransferData(this.amount);
+        return new TransferData(this.amount, this.extraParams);
       }
 
       /**
@@ -255,6 +309,32 @@ public Builder setAmount(Long amount) {
         this.amount = amount;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ChargeCaptureParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ChargeCaptureParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 }
diff --git a/src/main/java/com/stripe/param/ChargeCreateParams.java b/src/main/java/com/stripe/param/ChargeCreateParams.java
index 2757911f638..1131b287938 100644
--- a/src/main/java/com/stripe/param/ChargeCreateParams.java
+++ b/src/main/java/com/stripe/param/ChargeCreateParams.java
@@ -68,6 +68,15 @@ public class ChargeCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -154,6 +163,7 @@ private ChargeCreateParams(
       String description,
       Destination destination,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String onBehalfOf,
       String receiptEmail,
@@ -171,6 +181,7 @@ private ChargeCreateParams(
     this.description = description;
     this.destination = destination;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.onBehalfOf = onBehalfOf;
     this.receiptEmail = receiptEmail;
@@ -204,6 +215,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String onBehalfOf;
@@ -232,6 +245,7 @@ public ChargeCreateParams build() {
           this.description,
           this.destination,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.onBehalfOf,
           this.receiptEmail,
@@ -339,6 +353,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ChargeCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ChargeCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -462,9 +502,19 @@ public static class Destination {
     @SerializedName("amount")
     Long amount;
 
-    private Destination(String account, Long amount) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private Destination(String account, Long amount, Map<String, Object> extraParams) {
       this.account = account;
       this.amount = amount;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -476,9 +526,11 @@ public static class Builder {
 
       private Long amount;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public Destination build() {
-        return new Destination(this.account, this.amount);
+        return new Destination(this.account, this.amount, this.extraParams);
       }
 
       /** ID of an existing, connected Stripe account. */
@@ -496,6 +548,32 @@ public Builder setAmount(Long amount) {
         this.amount = amount;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ChargeCreateParams.Destination#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ChargeCreateParams.Destination#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 
@@ -508,6 +586,15 @@ public static class Shipping {
     @SerializedName("carrier")
     String carrier;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Recipient name. */
     @SerializedName("name")
     String name;
@@ -524,9 +611,15 @@ public static class Shipping {
     String trackingNumber;
 
     private Shipping(
-        Address address, String carrier, String name, String phone, String trackingNumber) {
+        Address address,
+        String carrier,
+        Map<String, Object> extraParams,
+        String name,
+        String phone,
+        String trackingNumber) {
       this.address = address;
       this.carrier = carrier;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
       this.trackingNumber = trackingNumber;
@@ -541,6 +634,8 @@ public static class Builder {
 
       private String carrier;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
@@ -549,7 +644,13 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.carrier, this.name, this.phone, this.trackingNumber);
+        return new Shipping(
+            this.address,
+            this.carrier,
+            this.extraParams,
+            this.name,
+            this.phone,
+            this.trackingNumber);
       }
 
       /** Shipping address. */
@@ -564,6 +665,32 @@ public Builder setCarrier(String carrier) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ChargeCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ChargeCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Recipient name. */
       public Builder setName(String name) {
         this.name = name;
@@ -593,6 +720,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -608,12 +744,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -629,6 +767,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -640,7 +780,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -653,6 +799,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link ChargeCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link ChargeCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
@@ -688,9 +862,19 @@ public static class TransferData {
     @SerializedName("destination")
     String destination;
 
-    private TransferData(Long amount, String destination) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private TransferData(Long amount, String destination, Map<String, Object> extraParams) {
       this.amount = amount;
       this.destination = destination;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -702,9 +886,11 @@ public static class Builder {
 
       private String destination;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public TransferData build() {
-        return new TransferData(this.amount, this.destination);
+        return new TransferData(this.amount, this.destination, this.extraParams);
       }
 
       /**
@@ -721,6 +907,32 @@ public Builder setDestination(String destination) {
         this.destination = destination;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ChargeCreateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ChargeCreateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 }
diff --git a/src/main/java/com/stripe/param/ChargeListParams.java b/src/main/java/com/stripe/param/ChargeListParams.java
index e7eb93578ca..5a6f26bdabd 100644
--- a/src/main/java/com/stripe/param/ChargeListParams.java
+++ b/src/main/java/com/stripe/param/ChargeListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ChargeListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -28,6 +30,15 @@ public class ChargeListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -35,6 +46,12 @@ public class ChargeListParams extends ApiRequestParams {
   @SerializedName("limit")
   Long limit;
 
+  /**
+   * Only return charges that were created by the PaymentIntent specified by this PaymentIntent ID.
+   */
+  @SerializedName("payment_intent")
+  String paymentIntent;
+
   /**
    * A cursor for use in pagination. `starting_after` is an object ID that defines your place in the
    * list. For instance, if you make a list request and receive 100 objects, ending with `obj_foo`,
@@ -53,14 +70,18 @@ private ChargeListParams(
       String customer,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
+      String paymentIntent,
       String startingAfter,
       String transferGroup) {
     this.created = created;
     this.customer = customer;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
+    this.paymentIntent = paymentIntent;
     this.startingAfter = startingAfter;
     this.transferGroup = transferGroup;
   }
@@ -78,8 +99,12 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
+    private String paymentIntent;
+
     private String startingAfter;
 
     private String transferGroup;
@@ -91,7 +116,9 @@ public ChargeListParams build() {
           this.customer,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
+          this.paymentIntent,
           this.startingAfter,
           this.transferGroup);
     }
@@ -149,6 +176,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ChargeListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ChargeListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -158,6 +211,15 @@ public Builder setLimit(Long limit) {
       return this;
     }
 
+    /**
+     * Only return charges that were created by the PaymentIntent specified by this PaymentIntent
+     * ID.
+     */
+    public Builder setPaymentIntent(String paymentIntent) {
+      this.paymentIntent = paymentIntent;
+      return this;
+    }
+
     /**
      * A cursor for use in pagination. `starting_after` is an object ID that defines your place in
      * the list. For instance, if you make a list request and receive 100 objects, ending with
@@ -177,6 +239,15 @@ public Builder setTransferGroup(String transferGroup) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -193,7 +264,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -205,6 +277,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -215,7 +289,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ChargeListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ChargeListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/ChargeRetrieveParams.java b/src/main/java/com/stripe/param/ChargeRetrieveParams.java
index 58b2cbf98fb..6303033b709 100644
--- a/src/main/java/com/stripe/param/ChargeRetrieveParams.java
+++ b/src/main/java/com/stripe/param/ChargeRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ChargeRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ChargeRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ChargeRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ChargeRetrieveParams build() {
-      return new ChargeRetrieveParams(this.expand);
+      return new ChargeRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ChargeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ChargeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/ChargeUpdateParams.java b/src/main/java/com/stripe/param/ChargeUpdateParams.java
index fb7d82846cf..1649857dce3 100644
--- a/src/main/java/com/stripe/param/ChargeUpdateParams.java
+++ b/src/main/java/com/stripe/param/ChargeUpdateParams.java
@@ -32,6 +32,15 @@ public class ChargeUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs you can attach to a charge giving information about its riskiness. If
    * you believe a charge is fraudulent, include a `user_report` key with a value of `fraudulent`.
@@ -73,6 +82,7 @@ private ChargeUpdateParams(
       String customer,
       String description,
       List<String> expand,
+      Map<String, Object> extraParams,
       FraudDetails fraudDetails,
       Map<String, String> metadata,
       String receiptEmail,
@@ -81,6 +91,7 @@ private ChargeUpdateParams(
     this.customer = customer;
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.fraudDetails = fraudDetails;
     this.metadata = metadata;
     this.receiptEmail = receiptEmail;
@@ -99,6 +110,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private FraudDetails fraudDetails;
 
     private Map<String, String> metadata;
@@ -115,6 +128,7 @@ public ChargeUpdateParams build() {
           this.customer,
           this.description,
           this.expand,
+          this.extraParams,
           this.fraudDetails,
           this.metadata,
           this.receiptEmail,
@@ -168,6 +182,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ChargeUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ChargeUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A set of key-value pairs you can attach to a charge giving information about its riskiness.
      * If you believe a charge is fraudulent, include a `user_report` key with a value of
@@ -233,10 +273,20 @@ public Builder setTransferGroup(String transferGroup) {
   }
 
   public static class FraudDetails {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("user_report")
     ApiRequestParams.EnumParam userReport;
 
-    private FraudDetails(ApiRequestParams.EnumParam userReport) {
+    private FraudDetails(Map<String, Object> extraParams, ApiRequestParams.EnumParam userReport) {
+      this.extraParams = extraParams;
       this.userReport = userReport;
     }
 
@@ -245,11 +295,39 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private ApiRequestParams.EnumParam userReport;
 
       /** Finalize and obtain parameter instance from this builder. */
       public FraudDetails build() {
-        return new FraudDetails(this.userReport);
+        return new FraudDetails(this.extraParams, this.userReport);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ChargeUpdateParams.FraudDetails#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ChargeUpdateParams.FraudDetails#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       public Builder setUserReport(UserReport userReport) {
@@ -288,6 +366,15 @@ public static class Shipping {
     @SerializedName("carrier")
     String carrier;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Recipient name. */
     @SerializedName("name")
     String name;
@@ -304,9 +391,15 @@ public static class Shipping {
     String trackingNumber;
 
     private Shipping(
-        Address address, String carrier, String name, String phone, String trackingNumber) {
+        Address address,
+        String carrier,
+        Map<String, Object> extraParams,
+        String name,
+        String phone,
+        String trackingNumber) {
       this.address = address;
       this.carrier = carrier;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
       this.trackingNumber = trackingNumber;
@@ -321,6 +414,8 @@ public static class Builder {
 
       private String carrier;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
@@ -329,7 +424,13 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.carrier, this.name, this.phone, this.trackingNumber);
+        return new Shipping(
+            this.address,
+            this.carrier,
+            this.extraParams,
+            this.name,
+            this.phone,
+            this.trackingNumber);
       }
 
       /** Shipping address. */
@@ -344,6 +445,32 @@ public Builder setCarrier(String carrier) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ChargeUpdateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ChargeUpdateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Recipient name. */
       public Builder setName(String name) {
         this.name = name;
@@ -373,6 +500,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -388,12 +524,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -409,6 +547,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -420,7 +560,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -433,6 +579,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link ChargeUpdateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link ChargeUpdateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
diff --git a/src/main/java/com/stripe/param/CountrySpecListParams.java b/src/main/java/com/stripe/param/CountrySpecListParams.java
index ba46a797c4f..a665cfdf6cb 100644
--- a/src/main/java/com/stripe/param/CountrySpecListParams.java
+++ b/src/main/java/com/stripe/param/CountrySpecListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CountrySpecListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class CountrySpecListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class CountrySpecListParams extends ApiRequestParams {
   String startingAfter;
 
   private CountrySpecListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public CountrySpecListParams build() {
       return new CountrySpecListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CountrySpecListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CountrySpecListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/CountrySpecRetrieveParams.java b/src/main/java/com/stripe/param/CountrySpecRetrieveParams.java
index cc235b1891d..cc35b6d0805 100644
--- a/src/main/java/com/stripe/param/CountrySpecRetrieveParams.java
+++ b/src/main/java/com/stripe/param/CountrySpecRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CountrySpecRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private CountrySpecRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private CountrySpecRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public CountrySpecRetrieveParams build() {
-      return new CountrySpecRetrieveParams(this.expand);
+      return new CountrySpecRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CountrySpecRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CountrySpecRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/CouponCreateParams.java b/src/main/java/com/stripe/param/CouponCreateParams.java
index cdc47fb86d0..c5db64bc05d 100644
--- a/src/main/java/com/stripe/param/CouponCreateParams.java
+++ b/src/main/java/com/stripe/param/CouponCreateParams.java
@@ -43,6 +43,15 @@ public class CouponCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Unique string of your choice that will be used to identify this coupon when applying it to a
    * customer. This is often a specific code you'll give to your customer to use when signing up
@@ -94,6 +103,7 @@ private CouponCreateParams(
       Duration duration,
       Long durationInMonths,
       List<String> expand,
+      Map<String, Object> extraParams,
       String id,
       Long maxRedemptions,
       Map<String, String> metadata,
@@ -105,6 +115,7 @@ private CouponCreateParams(
     this.duration = duration;
     this.durationInMonths = durationInMonths;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.id = id;
     this.maxRedemptions = maxRedemptions;
     this.metadata = metadata;
@@ -128,6 +139,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String id;
 
     private Long maxRedemptions;
@@ -148,6 +161,7 @@ public CouponCreateParams build() {
           this.duration,
           this.durationInMonths,
           this.expand,
+          this.extraParams,
           this.id,
           this.maxRedemptions,
           this.metadata,
@@ -217,6 +231,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CouponCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CouponCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Unique string of your choice that will be used to identify this coupon when applying it to a
      * customer. This is often a specific code you'll give to your customer to use when signing up
diff --git a/src/main/java/com/stripe/param/CouponListParams.java b/src/main/java/com/stripe/param/CouponListParams.java
index 93a1a008fbc..74cff1997f5 100644
--- a/src/main/java/com/stripe/param/CouponListParams.java
+++ b/src/main/java/com/stripe/param/CouponListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CouponListParams extends ApiRequestParams {
   /**
@@ -28,6 +30,15 @@ public class CouponListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -45,10 +56,16 @@ public class CouponListParams extends ApiRequestParams {
   String startingAfter;
 
   private CouponListParams(
-      Object created, String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      Object created,
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -64,6 +81,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -71,7 +90,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public CouponListParams build() {
       return new CouponListParams(
-          this.created, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.created,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     /**
@@ -129,6 +153,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CouponListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CouponListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -151,6 +201,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -167,7 +226,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -179,6 +239,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -189,7 +251,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CouponListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CouponListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/CouponRetrieveParams.java b/src/main/java/com/stripe/param/CouponRetrieveParams.java
index 34d188bc62d..9c92adc8b27 100644
--- a/src/main/java/com/stripe/param/CouponRetrieveParams.java
+++ b/src/main/java/com/stripe/param/CouponRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CouponRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private CouponRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private CouponRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public CouponRetrieveParams build() {
-      return new CouponRetrieveParams(this.expand);
+      return new CouponRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CouponRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CouponRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/CouponUpdateParams.java b/src/main/java/com/stripe/param/CouponUpdateParams.java
index 637ae651e3b..f28f476ab4e 100644
--- a/src/main/java/com/stripe/param/CouponUpdateParams.java
+++ b/src/main/java/com/stripe/param/CouponUpdateParams.java
@@ -14,6 +14,15 @@ public class CouponUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to a coupon object. It can be useful for storing
    * additional information about the coupon in a structured format.
@@ -28,8 +37,13 @@ public class CouponUpdateParams extends ApiRequestParams {
   @SerializedName("name")
   String name;
 
-  private CouponUpdateParams(List<String> expand, Map<String, String> metadata, String name) {
+  private CouponUpdateParams(
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata,
+      String name) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.name = name;
   }
@@ -41,13 +55,15 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String name;
 
     /** Finalize and obtain parameter instance from this builder. */
     public CouponUpdateParams build() {
-      return new CouponUpdateParams(this.expand, this.metadata, this.name);
+      return new CouponUpdateParams(this.expand, this.extraParams, this.metadata, this.name);
     }
 
     /**
@@ -76,6 +92,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CouponUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CouponUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/CreditNoteCreateParams.java b/src/main/java/com/stripe/param/CreditNoteCreateParams.java
index 920a5e27535..d272933a146 100644
--- a/src/main/java/com/stripe/param/CreditNoteCreateParams.java
+++ b/src/main/java/com/stripe/param/CreditNoteCreateParams.java
@@ -26,6 +26,15 @@ public class CreditNoteCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** ID of the invoice. */
   @SerializedName("invoice")
   String invoice;
@@ -64,6 +73,7 @@ private CreditNoteCreateParams(
       Long amount,
       Long creditAmount,
       List<String> expand,
+      Map<String, Object> extraParams,
       String invoice,
       String memo,
       Map<String, String> metadata,
@@ -73,6 +83,7 @@ private CreditNoteCreateParams(
     this.amount = amount;
     this.creditAmount = creditAmount;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoice = invoice;
     this.memo = memo;
     this.metadata = metadata;
@@ -92,6 +103,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String invoice;
 
     private String memo;
@@ -110,6 +123,7 @@ public CreditNoteCreateParams build() {
           this.amount,
           this.creditAmount,
           this.expand,
+          this.extraParams,
           this.invoice,
           this.memo,
           this.metadata,
@@ -159,6 +173,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CreditNoteCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CreditNoteCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** ID of the invoice. */
     public Builder setInvoice(String invoice) {
       this.invoice = invoice;
diff --git a/src/main/java/com/stripe/param/CreditNoteListParams.java b/src/main/java/com/stripe/param/CreditNoteListParams.java
index 0f7256e5dc8..a0365e52b41 100644
--- a/src/main/java/com/stripe/param/CreditNoteListParams.java
+++ b/src/main/java/com/stripe/param/CreditNoteListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CreditNoteListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class CreditNoteListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** ID of the invoice. */
   @SerializedName("invoice")
   String invoice;
@@ -42,9 +53,15 @@ public class CreditNoteListParams extends ApiRequestParams {
   String startingAfter;
 
   private CreditNoteListParams(
-      String endingBefore, List<String> expand, String invoice, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      String invoice,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoice = invoice;
     this.limit = limit;
     this.startingAfter = startingAfter;
@@ -59,6 +76,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String invoice;
 
     private Long limit;
@@ -68,7 +87,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public CreditNoteListParams build() {
       return new CreditNoteListParams(
-          this.endingBefore, this.expand, this.invoice, this.limit, this.startingAfter);
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.invoice,
+          this.limit,
+          this.startingAfter);
     }
 
     /**
@@ -108,6 +132,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CreditNoteListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CreditNoteListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** ID of the invoice. */
     public Builder setInvoice(String invoice) {
       this.invoice = invoice;
diff --git a/src/main/java/com/stripe/param/CreditNoteRetrieveParams.java b/src/main/java/com/stripe/param/CreditNoteRetrieveParams.java
index 5c664e9ad38..3e875c0a75c 100644
--- a/src/main/java/com/stripe/param/CreditNoteRetrieveParams.java
+++ b/src/main/java/com/stripe/param/CreditNoteRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CreditNoteRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private CreditNoteRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private CreditNoteRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public CreditNoteRetrieveParams build() {
-      return new CreditNoteRetrieveParams(this.expand);
+      return new CreditNoteRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CreditNoteRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CreditNoteRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/CreditNoteUpdateParams.java b/src/main/java/com/stripe/param/CreditNoteUpdateParams.java
index bfb0d9652da..a5ad2096e0e 100644
--- a/src/main/java/com/stripe/param/CreditNoteUpdateParams.java
+++ b/src/main/java/com/stripe/param/CreditNoteUpdateParams.java
@@ -14,6 +14,15 @@ public class CreditNoteUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Credit note memo. */
   @SerializedName("memo")
   String memo;
@@ -26,8 +35,13 @@ public class CreditNoteUpdateParams extends ApiRequestParams {
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private CreditNoteUpdateParams(List<String> expand, String memo, Map<String, String> metadata) {
+  private CreditNoteUpdateParams(
+      List<String> expand,
+      Map<String, Object> extraParams,
+      String memo,
+      Map<String, String> metadata) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.memo = memo;
     this.metadata = metadata;
   }
@@ -39,13 +53,15 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String memo;
 
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public CreditNoteUpdateParams build() {
-      return new CreditNoteUpdateParams(this.expand, this.memo, this.metadata);
+      return new CreditNoteUpdateParams(this.expand, this.extraParams, this.memo, this.metadata);
     }
 
     /**
@@ -74,6 +90,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CreditNoteUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CreditNoteUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Credit note memo. */
     public Builder setMemo(String memo) {
       this.memo = memo;
diff --git a/src/main/java/com/stripe/param/CreditNoteVoidCreditNoteParams.java b/src/main/java/com/stripe/param/CreditNoteVoidCreditNoteParams.java
index f39935b5f13..4842e163cbd 100644
--- a/src/main/java/com/stripe/param/CreditNoteVoidCreditNoteParams.java
+++ b/src/main/java/com/stripe/param/CreditNoteVoidCreditNoteParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CreditNoteVoidCreditNoteParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private CreditNoteVoidCreditNoteParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private CreditNoteVoidCreditNoteParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public CreditNoteVoidCreditNoteParams build() {
-      return new CreditNoteVoidCreditNoteParams(this.expand);
+      return new CreditNoteVoidCreditNoteParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CreditNoteVoidCreditNoteParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CreditNoteVoidCreditNoteParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/CustomerCreateParams.java b/src/main/java/com/stripe/param/CustomerCreateParams.java
index 3ff4b514d14..8b94e8763d1 100644
--- a/src/main/java/com/stripe/param/CustomerCreateParams.java
+++ b/src/main/java/com/stripe/param/CustomerCreateParams.java
@@ -45,6 +45,15 @@ public class CustomerCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * The prefix for the customer used to generate unique invoice numbers. Must be 3–12 uppercase
    * letters or numbers.
@@ -109,6 +118,7 @@ private CustomerCreateParams(
       String description,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       String invoicePrefix,
       InvoiceSettings invoiceSettings,
       Map<String, String> metadata,
@@ -127,6 +137,7 @@ private CustomerCreateParams(
     this.description = description;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoicePrefix = invoicePrefix;
     this.invoiceSettings = invoiceSettings;
     this.metadata = metadata;
@@ -158,6 +169,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String invoicePrefix;
 
     private InvoiceSettings invoiceSettings;
@@ -191,6 +204,7 @@ public CustomerCreateParams build() {
           this.description,
           this.email,
           this.expand,
+          this.extraParams,
           this.invoicePrefix,
           this.invoiceSettings,
           this.metadata,
@@ -276,6 +290,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CustomerCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CustomerCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * The prefix for the customer used to generate unique invoice numbers. Must be 3–12 uppercase
      * letters or numbers.
@@ -434,6 +474,15 @@ public static class Address {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("line1")
     String line1;
 
@@ -447,9 +496,16 @@ public static class Address {
     String state;
 
     private Address(
-        String city, String country, String line1, String line2, String postalCode, String state) {
+        String city,
+        String country,
+        Map<String, Object> extraParams,
+        String line1,
+        String line2,
+        String postalCode,
+        String state) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -465,6 +521,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -476,7 +534,13 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Address build() {
         return new Address(
-            this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+            this.city,
+            this.country,
+            this.extraParams,
+            this.line1,
+            this.line2,
+            this.postalCode,
+            this.state);
       }
 
       public Builder setCity(String city) {
@@ -489,6 +553,32 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerCreateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerCreateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       public Builder setLine1(String line1) {
         this.line1 = line1;
         return this;
@@ -520,13 +610,27 @@ public static class InvoiceSettings {
     @SerializedName("default_payment_method")
     String defaultPaymentMethod;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Default footer to be displayed on invoices for this customer. */
     @SerializedName("footer")
     String footer;
 
-    private InvoiceSettings(Object customFields, String defaultPaymentMethod, String footer) {
+    private InvoiceSettings(
+        Object customFields,
+        String defaultPaymentMethod,
+        Map<String, Object> extraParams,
+        String footer) {
       this.customFields = customFields;
       this.defaultPaymentMethod = defaultPaymentMethod;
+      this.extraParams = extraParams;
       this.footer = footer;
     }
 
@@ -539,11 +643,14 @@ public static class Builder {
 
       private String defaultPaymentMethod;
 
+      private Map<String, Object> extraParams;
+
       private String footer;
 
       /** Finalize and obtain parameter instance from this builder. */
       public InvoiceSettings build() {
-        return new InvoiceSettings(this.customFields, this.defaultPaymentMethod, this.footer);
+        return new InvoiceSettings(
+            this.customFields, this.defaultPaymentMethod, this.extraParams, this.footer);
       }
 
       /** Default custom fields to be displayed on invoices for this customer. */
@@ -564,6 +671,32 @@ public Builder setDefaultPaymentMethod(String defaultPaymentMethod) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerCreateParams.InvoiceSettings#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerCreateParams.InvoiceSettings#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Default footer to be displayed on invoices for this customer. */
       public Builder setFooter(String footer) {
         this.footer = footer;
@@ -572,6 +705,15 @@ public Builder setFooter(String footer) {
     }
 
     public static class CustomField {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** The name of the custom field. This may be up to 30 characters. */
       @SerializedName("name")
       String name;
@@ -580,7 +722,8 @@ public static class CustomField {
       @SerializedName("value")
       String value;
 
-      private CustomField(String name, String value) {
+      private CustomField(Map<String, Object> extraParams, String name, String value) {
+        this.extraParams = extraParams;
         this.name = name;
         this.value = value;
       }
@@ -590,13 +733,43 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private String name;
 
         private String value;
 
         /** Finalize and obtain parameter instance from this builder. */
         public CustomField build() {
-          return new CustomField(this.name, this.value);
+          return new CustomField(this.extraParams, this.name, this.value);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CustomerCreateParams.InvoiceSettings.CustomField#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CustomerCreateParams.InvoiceSettings.CustomField#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** The name of the custom field. This may be up to 30 characters. */
@@ -619,6 +792,15 @@ public static class Shipping {
     @SerializedName("address")
     Address address;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Customer name. */
     @SerializedName("name")
     String name;
@@ -627,8 +809,9 @@ public static class Shipping {
     @SerializedName("phone")
     String phone;
 
-    private Shipping(Address address, String name, String phone) {
+    private Shipping(Address address, Map<String, Object> extraParams, String name, String phone) {
       this.address = address;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
     }
@@ -640,13 +823,15 @@ public static Builder builder() {
     public static class Builder {
       private Address address;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.name, this.phone);
+        return new Shipping(this.address, this.extraParams, this.name, this.phone);
       }
 
       /** Customer shipping address. */
@@ -655,6 +840,32 @@ public Builder setAddress(Address address) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Customer name. */
       public Builder setName(String name) {
         this.name = name;
@@ -675,6 +886,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -690,12 +910,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -711,6 +933,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -722,7 +946,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -735,6 +965,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CustomerCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CustomerCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
@@ -759,6 +1017,15 @@ public Builder setState(String state) {
   }
 
   public static class TaxIdData {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Type of the tax ID, one of `eu_vat`, `nz_gst`, or `au_abn`. */
     @SerializedName("type")
     Type type;
@@ -767,7 +1034,8 @@ public static class TaxIdData {
     @SerializedName("value")
     String value;
 
-    private TaxIdData(Type type, String value) {
+    private TaxIdData(Map<String, Object> extraParams, Type type, String value) {
+      this.extraParams = extraParams;
       this.type = type;
       this.value = value;
     }
@@ -777,13 +1045,41 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Type type;
 
       private String value;
 
       /** Finalize and obtain parameter instance from this builder. */
       public TaxIdData build() {
-        return new TaxIdData(this.type, this.value);
+        return new TaxIdData(this.extraParams, this.type, this.value);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerCreateParams.TaxIdData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerCreateParams.TaxIdData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Type of the tax ID, one of `eu_vat`, `nz_gst`, or `au_abn`. */
@@ -819,6 +1115,15 @@ public enum Type implements ApiRequestParams.EnumParam {
   }
 
   public static class TaxInfo {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The customer's tax ID number. */
     @SerializedName("tax_id")
     String taxId;
@@ -827,7 +1132,8 @@ public static class TaxInfo {
     @SerializedName("type")
     Type type;
 
-    private TaxInfo(String taxId, Type type) {
+    private TaxInfo(Map<String, Object> extraParams, String taxId, Type type) {
+      this.extraParams = extraParams;
       this.taxId = taxId;
       this.type = type;
     }
@@ -837,13 +1143,41 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String taxId;
 
       private Type type;
 
       /** Finalize and obtain parameter instance from this builder. */
       public TaxInfo build() {
-        return new TaxInfo(this.taxId, this.type);
+        return new TaxInfo(this.extraParams, this.taxId, this.type);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerCreateParams.TaxInfo#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerCreateParams.TaxInfo#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** The customer's tax ID number. */
diff --git a/src/main/java/com/stripe/param/CustomerListParams.java b/src/main/java/com/stripe/param/CustomerListParams.java
index ab42f0f7729..31141608a9a 100644
--- a/src/main/java/com/stripe/param/CustomerListParams.java
+++ b/src/main/java/com/stripe/param/CustomerListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CustomerListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -28,6 +30,15 @@ public class CustomerListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -49,12 +60,14 @@ private CustomerListParams(
       String email,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter) {
     this.created = created;
     this.email = email;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -72,6 +85,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -79,7 +94,13 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public CustomerListParams build() {
       return new CustomerListParams(
-          this.created, this.email, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.created,
+          this.email,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     public Builder setCreated(Created created) {
@@ -135,6 +156,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CustomerListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CustomerListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -157,6 +204,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -173,7 +229,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -185,6 +242,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -195,7 +254,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/CustomerRetrieveParams.java b/src/main/java/com/stripe/param/CustomerRetrieveParams.java
index eb60d682cec..86a4cc5b9f4 100644
--- a/src/main/java/com/stripe/param/CustomerRetrieveParams.java
+++ b/src/main/java/com/stripe/param/CustomerRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CustomerRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private CustomerRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private CustomerRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public CustomerRetrieveParams build() {
-      return new CustomerRetrieveParams(this.expand);
+      return new CustomerRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CustomerRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CustomerRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/CustomerUpdateParams.java b/src/main/java/com/stripe/param/CustomerUpdateParams.java
index 0b4c908af1d..af1f5aaaeae 100644
--- a/src/main/java/com/stripe/param/CustomerUpdateParams.java
+++ b/src/main/java/com/stripe/param/CustomerUpdateParams.java
@@ -53,6 +53,15 @@ public class CustomerUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * The prefix for the customer used to generate unique invoice numbers. Must be 3–12 uppercase
    * letters or numbers.
@@ -121,6 +130,7 @@ private CustomerUpdateParams(
       String description,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       String invoicePrefix,
       InvoiceSettings invoiceSettings,
       Map<String, String> metadata,
@@ -139,6 +149,7 @@ private CustomerUpdateParams(
     this.description = description;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoicePrefix = invoicePrefix;
     this.invoiceSettings = invoiceSettings;
     this.metadata = metadata;
@@ -171,6 +182,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String invoicePrefix;
 
     private InvoiceSettings invoiceSettings;
@@ -203,6 +216,7 @@ public CustomerUpdateParams build() {
           this.description,
           this.email,
           this.expand,
+          this.extraParams,
           this.invoicePrefix,
           this.invoiceSettings,
           this.metadata,
@@ -298,6 +312,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CustomerUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CustomerUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * The prefix for the customer used to generate unique invoice numbers. Must be 3–12 uppercase
      * letters or numbers.
@@ -449,6 +489,15 @@ public static class Address {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("line1")
     String line1;
 
@@ -462,9 +511,16 @@ public static class Address {
     String state;
 
     private Address(
-        String city, String country, String line1, String line2, String postalCode, String state) {
+        String city,
+        String country,
+        Map<String, Object> extraParams,
+        String line1,
+        String line2,
+        String postalCode,
+        String state) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -480,6 +536,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -491,7 +549,13 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Address build() {
         return new Address(
-            this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+            this.city,
+            this.country,
+            this.extraParams,
+            this.line1,
+            this.line2,
+            this.postalCode,
+            this.state);
       }
 
       public Builder setCity(String city) {
@@ -504,6 +568,32 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerUpdateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerUpdateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       public Builder setLine1(String line1) {
         this.line1 = line1;
         return this;
@@ -535,13 +625,27 @@ public static class InvoiceSettings {
     @SerializedName("default_payment_method")
     String defaultPaymentMethod;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Default footer to be displayed on invoices for this customer. */
     @SerializedName("footer")
     String footer;
 
-    private InvoiceSettings(Object customFields, String defaultPaymentMethod, String footer) {
+    private InvoiceSettings(
+        Object customFields,
+        String defaultPaymentMethod,
+        Map<String, Object> extraParams,
+        String footer) {
       this.customFields = customFields;
       this.defaultPaymentMethod = defaultPaymentMethod;
+      this.extraParams = extraParams;
       this.footer = footer;
     }
 
@@ -554,11 +658,14 @@ public static class Builder {
 
       private String defaultPaymentMethod;
 
+      private Map<String, Object> extraParams;
+
       private String footer;
 
       /** Finalize and obtain parameter instance from this builder. */
       public InvoiceSettings build() {
-        return new InvoiceSettings(this.customFields, this.defaultPaymentMethod, this.footer);
+        return new InvoiceSettings(
+            this.customFields, this.defaultPaymentMethod, this.extraParams, this.footer);
       }
 
       /** Default custom fields to be displayed on invoices for this customer. */
@@ -579,6 +686,32 @@ public Builder setDefaultPaymentMethod(String defaultPaymentMethod) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerUpdateParams.InvoiceSettings#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerUpdateParams.InvoiceSettings#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Default footer to be displayed on invoices for this customer. */
       public Builder setFooter(String footer) {
         this.footer = footer;
@@ -587,6 +720,15 @@ public Builder setFooter(String footer) {
     }
 
     public static class CustomField {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** The name of the custom field. This may be up to 30 characters. */
       @SerializedName("name")
       String name;
@@ -595,7 +737,8 @@ public static class CustomField {
       @SerializedName("value")
       String value;
 
-      private CustomField(String name, String value) {
+      private CustomField(Map<String, Object> extraParams, String name, String value) {
+        this.extraParams = extraParams;
         this.name = name;
         this.value = value;
       }
@@ -605,13 +748,43 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private String name;
 
         private String value;
 
         /** Finalize and obtain parameter instance from this builder. */
         public CustomField build() {
-          return new CustomField(this.name, this.value);
+          return new CustomField(this.extraParams, this.name, this.value);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CustomerUpdateParams.InvoiceSettings.CustomField#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CustomerUpdateParams.InvoiceSettings.CustomField#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** The name of the custom field. This may be up to 30 characters. */
@@ -634,6 +807,15 @@ public static class Shipping {
     @SerializedName("address")
     Address address;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Customer name. */
     @SerializedName("name")
     String name;
@@ -642,8 +824,9 @@ public static class Shipping {
     @SerializedName("phone")
     String phone;
 
-    private Shipping(Address address, String name, String phone) {
+    private Shipping(Address address, Map<String, Object> extraParams, String name, String phone) {
       this.address = address;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
     }
@@ -655,13 +838,15 @@ public static Builder builder() {
     public static class Builder {
       private Address address;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.name, this.phone);
+        return new Shipping(this.address, this.extraParams, this.name, this.phone);
       }
 
       /** Customer shipping address. */
@@ -670,6 +855,32 @@ public Builder setAddress(Address address) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerUpdateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerUpdateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Customer name. */
       public Builder setName(String name) {
         this.name = name;
@@ -690,6 +901,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -705,12 +925,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -726,6 +948,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -737,7 +961,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -750,6 +980,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CustomerUpdateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CustomerUpdateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
@@ -774,6 +1032,15 @@ public Builder setState(String state) {
   }
 
   public static class TaxInfo {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The customer's tax ID number. */
     @SerializedName("tax_id")
     String taxId;
@@ -782,7 +1049,8 @@ public static class TaxInfo {
     @SerializedName("type")
     Type type;
 
-    private TaxInfo(String taxId, Type type) {
+    private TaxInfo(Map<String, Object> extraParams, String taxId, Type type) {
+      this.extraParams = extraParams;
       this.taxId = taxId;
       this.type = type;
     }
@@ -792,13 +1060,41 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String taxId;
 
       private Type type;
 
       /** Finalize and obtain parameter instance from this builder. */
       public TaxInfo build() {
-        return new TaxInfo(this.taxId, this.type);
+        return new TaxInfo(this.extraParams, this.taxId, this.type);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CustomerUpdateParams.TaxInfo#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CustomerUpdateParams.TaxInfo#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** The customer's tax ID number. */
diff --git a/src/main/java/com/stripe/param/DisputeCloseParams.java b/src/main/java/com/stripe/param/DisputeCloseParams.java
index a3d2a68921d..9d562002211 100644
--- a/src/main/java/com/stripe/param/DisputeCloseParams.java
+++ b/src/main/java/com/stripe/param/DisputeCloseParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class DisputeCloseParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private DisputeCloseParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private DisputeCloseParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public DisputeCloseParams build() {
-      return new DisputeCloseParams(this.expand);
+      return new DisputeCloseParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * DisputeCloseParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link DisputeCloseParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/DisputeListParams.java b/src/main/java/com/stripe/param/DisputeListParams.java
index 208cd8e6cc5..3f214049f76 100644
--- a/src/main/java/com/stripe/param/DisputeListParams.java
+++ b/src/main/java/com/stripe/param/DisputeListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class DisputeListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -24,6 +26,15 @@ public class DisputeListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -41,10 +52,16 @@ public class DisputeListParams extends ApiRequestParams {
   String startingAfter;
 
   private DisputeListParams(
-      Object created, String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      Object created,
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -60,6 +77,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -67,7 +86,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public DisputeListParams build() {
       return new DisputeListParams(
-          this.created, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.created,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     public Builder setCreated(Created created) {
@@ -117,6 +141,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * DisputeListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link DisputeListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -139,6 +189,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -155,7 +214,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -167,6 +227,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -177,7 +239,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * DisputeListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link DisputeListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/DisputeRetrieveParams.java b/src/main/java/com/stripe/param/DisputeRetrieveParams.java
index da538802b43..c79453fab75 100644
--- a/src/main/java/com/stripe/param/DisputeRetrieveParams.java
+++ b/src/main/java/com/stripe/param/DisputeRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class DisputeRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private DisputeRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private DisputeRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public DisputeRetrieveParams build() {
-      return new DisputeRetrieveParams(this.expand);
+      return new DisputeRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * DisputeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link DisputeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/DisputeUpdateParams.java b/src/main/java/com/stripe/param/DisputeUpdateParams.java
index d5974ab6df4..530b7654fb5 100644
--- a/src/main/java/com/stripe/param/DisputeUpdateParams.java
+++ b/src/main/java/com/stripe/param/DisputeUpdateParams.java
@@ -22,6 +22,15 @@ public class DisputeUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to a dispute object. This can be useful for
    * storing additional information about the dispute in a structured format.
@@ -38,9 +47,14 @@ public class DisputeUpdateParams extends ApiRequestParams {
   Boolean submit;
 
   private DisputeUpdateParams(
-      Evidence evidence, List<String> expand, Map<String, String> metadata, Boolean submit) {
+      Evidence evidence,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata,
+      Boolean submit) {
     this.evidence = evidence;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.submit = submit;
   }
@@ -54,13 +68,16 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private Boolean submit;
 
     /** Finalize and obtain parameter instance from this builder. */
     public DisputeUpdateParams build() {
-      return new DisputeUpdateParams(this.evidence, this.expand, this.metadata, this.submit);
+      return new DisputeUpdateParams(
+          this.evidence, this.expand, this.extraParams, this.metadata, this.submit);
     }
 
     /**
@@ -99,6 +116,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * DisputeUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link DisputeUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -180,6 +223,15 @@ public static class Evidence {
     @SerializedName("duplicate_charge_id")
     String duplicateChargeId;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Has a maximum character count of 20,000. */
     @SerializedName("product_description")
     String productDescription;
@@ -240,6 +292,7 @@ private Evidence(
         String duplicateChargeDocumentation,
         String duplicateChargeExplanation,
         String duplicateChargeId,
+        Map<String, Object> extraParams,
         String productDescription,
         String receipt,
         String refundPolicy,
@@ -267,6 +320,7 @@ private Evidence(
       this.duplicateChargeDocumentation = duplicateChargeDocumentation;
       this.duplicateChargeExplanation = duplicateChargeExplanation;
       this.duplicateChargeId = duplicateChargeId;
+      this.extraParams = extraParams;
       this.productDescription = productDescription;
       this.receipt = receipt;
       this.refundPolicy = refundPolicy;
@@ -314,6 +368,8 @@ public static class Builder {
 
       private String duplicateChargeId;
 
+      private Map<String, Object> extraParams;
+
       private String productDescription;
 
       private String receipt;
@@ -358,6 +414,7 @@ public Evidence build() {
             this.duplicateChargeDocumentation,
             this.duplicateChargeExplanation,
             this.duplicateChargeId,
+            this.extraParams,
             this.productDescription,
             this.receipt,
             this.refundPolicy,
@@ -443,6 +500,32 @@ public Builder setDuplicateChargeId(String duplicateChargeId) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * DisputeUpdateParams.Evidence#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link DisputeUpdateParams.Evidence#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Has a maximum character count of 20,000. */
       public Builder setProductDescription(String productDescription) {
         this.productDescription = productDescription;
diff --git a/src/main/java/com/stripe/param/ExchangeRateListParams.java b/src/main/java/com/stripe/param/ExchangeRateListParams.java
index 19f2d0a01a2..ae843acfb97 100644
--- a/src/main/java/com/stripe/param/ExchangeRateListParams.java
+++ b/src/main/java/com/stripe/param/ExchangeRateListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ExchangeRateListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class ExchangeRateListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and total number of
    * supported payout currencies, and the default is the max.
@@ -38,9 +49,14 @@ public class ExchangeRateListParams extends ApiRequestParams {
   String startingAfter;
 
   private ExchangeRateListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public ExchangeRateListParams build() {
       return new ExchangeRateListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ExchangeRateListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ExchangeRateListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and total number
      * of supported payout currencies, and the default is the max.
diff --git a/src/main/java/com/stripe/param/ExchangeRateRetrieveParams.java b/src/main/java/com/stripe/param/ExchangeRateRetrieveParams.java
index 8a21e33dc67..c3254d512a6 100644
--- a/src/main/java/com/stripe/param/ExchangeRateRetrieveParams.java
+++ b/src/main/java/com/stripe/param/ExchangeRateRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ExchangeRateRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ExchangeRateRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ExchangeRateRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ExchangeRateRetrieveParams build() {
-      return new ExchangeRateRetrieveParams(this.expand);
+      return new ExchangeRateRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ExchangeRateRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ExchangeRateRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/ExternalAccountCollectionCreateParams.java b/src/main/java/com/stripe/param/ExternalAccountCollectionCreateParams.java
index f0efe6897a7..06fef71adec 100644
--- a/src/main/java/com/stripe/param/ExternalAccountCollectionCreateParams.java
+++ b/src/main/java/com/stripe/param/ExternalAccountCollectionCreateParams.java
@@ -25,6 +25,15 @@ public class ExternalAccountCollectionCreateParams extends ApiRequestParams {
   @SerializedName("external_account")
   String externalAccount;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to an external account object. It can be useful
    * for storing additional information about the external account in a structured format.
@@ -36,10 +45,12 @@ private ExternalAccountCollectionCreateParams(
       Boolean defaultForCurrency,
       List<String> expand,
       String externalAccount,
+      Map<String, Object> extraParams,
       Map<String, String> metadata) {
     this.defaultForCurrency = defaultForCurrency;
     this.expand = expand;
     this.externalAccount = externalAccount;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -54,12 +65,18 @@ public static class Builder {
 
     private String externalAccount;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ExternalAccountCollectionCreateParams build() {
       return new ExternalAccountCollectionCreateParams(
-          this.defaultForCurrency, this.expand, this.externalAccount, this.metadata);
+          this.defaultForCurrency,
+          this.expand,
+          this.externalAccount,
+          this.extraParams,
+          this.metadata);
     }
 
     /**
@@ -103,6 +120,32 @@ public Builder setExternalAccount(String externalAccount) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ExternalAccountCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ExternalAccountCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/ExternalAccountCollectionListParams.java b/src/main/java/com/stripe/param/ExternalAccountCollectionListParams.java
index 9543b42e01a..e27b3c2d883 100644
--- a/src/main/java/com/stripe/param/ExternalAccountCollectionListParams.java
+++ b/src/main/java/com/stripe/param/ExternalAccountCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ExternalAccountCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class ExternalAccountCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class ExternalAccountCollectionListParams extends ApiRequestParams {
   String startingAfter;
 
   private ExternalAccountCollectionListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public ExternalAccountCollectionListParams build() {
       return new ExternalAccountCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ExternalAccountCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ExternalAccountCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/ExternalAccountCollectionRetrieveParams.java b/src/main/java/com/stripe/param/ExternalAccountCollectionRetrieveParams.java
index b4e97b402db..0a36b077747 100644
--- a/src/main/java/com/stripe/param/ExternalAccountCollectionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/ExternalAccountCollectionRetrieveParams.java
@@ -5,15 +5,28 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ExternalAccountCollectionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ExternalAccountCollectionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ExternalAccountCollectionRetrieveParams(
+      List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +36,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ExternalAccountCollectionRetrieveParams build() {
-      return new ExternalAccountCollectionRetrieveParams(this.expand);
+      return new ExternalAccountCollectionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +68,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ExternalAccountCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ExternalAccountCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/ExternalAccountUpdateParams.java b/src/main/java/com/stripe/param/ExternalAccountUpdateParams.java
index 12eb7fd13d8..7277b5359c2 100644
--- a/src/main/java/com/stripe/param/ExternalAccountUpdateParams.java
+++ b/src/main/java/com/stripe/param/ExternalAccountUpdateParams.java
@@ -60,6 +60,15 @@ public class ExternalAccountUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
@@ -80,6 +89,7 @@ private ExternalAccountUpdateParams(
       String expMonth,
       String expYear,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String name) {
     this.accountHolderName = accountHolderName;
@@ -94,6 +104,7 @@ private ExternalAccountUpdateParams(
     this.expMonth = expMonth;
     this.expYear = expYear;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.name = name;
   }
@@ -127,6 +138,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String name;
@@ -146,6 +159,7 @@ public ExternalAccountUpdateParams build() {
           this.expMonth,
           this.expYear,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.name);
     }
@@ -248,6 +262,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ExternalAccountUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ExternalAccountUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/FeeRefundCollectionCreateParams.java b/src/main/java/com/stripe/param/FeeRefundCollectionCreateParams.java
index b4ae6e44efb..5cafa8032bf 100644
--- a/src/main/java/com/stripe/param/FeeRefundCollectionCreateParams.java
+++ b/src/main/java/com/stripe/param/FeeRefundCollectionCreateParams.java
@@ -21,6 +21,15 @@ public class FeeRefundCollectionCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -30,9 +39,13 @@ public class FeeRefundCollectionCreateParams extends ApiRequestParams {
   Map<String, String> metadata;
 
   private FeeRefundCollectionCreateParams(
-      Long amount, List<String> expand, Map<String, String> metadata) {
+      Long amount,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata) {
     this.amount = amount;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -45,11 +58,14 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public FeeRefundCollectionCreateParams build() {
-      return new FeeRefundCollectionCreateParams(this.amount, this.expand, this.metadata);
+      return new FeeRefundCollectionCreateParams(
+          this.amount, this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -87,6 +103,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * FeeRefundCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link FeeRefundCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/FeeRefundCollectionListParams.java b/src/main/java/com/stripe/param/FeeRefundCollectionListParams.java
index cb26b44a580..cd0499c903d 100644
--- a/src/main/java/com/stripe/param/FeeRefundCollectionListParams.java
+++ b/src/main/java/com/stripe/param/FeeRefundCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class FeeRefundCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class FeeRefundCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class FeeRefundCollectionListParams extends ApiRequestParams {
   String startingAfter;
 
   private FeeRefundCollectionListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public FeeRefundCollectionListParams build() {
       return new FeeRefundCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * FeeRefundCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link FeeRefundCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/FeeRefundCollectionRetrieveParams.java b/src/main/java/com/stripe/param/FeeRefundCollectionRetrieveParams.java
index cd3df7a3c36..79a93c5b97b 100644
--- a/src/main/java/com/stripe/param/FeeRefundCollectionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/FeeRefundCollectionRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class FeeRefundCollectionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private FeeRefundCollectionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private FeeRefundCollectionRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public FeeRefundCollectionRetrieveParams build() {
-      return new FeeRefundCollectionRetrieveParams(this.expand);
+      return new FeeRefundCollectionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * FeeRefundCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link FeeRefundCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/FeeRefundUpdateParams.java b/src/main/java/com/stripe/param/FeeRefundUpdateParams.java
index f0c7b43196d..e6f053a849d 100644
--- a/src/main/java/com/stripe/param/FeeRefundUpdateParams.java
+++ b/src/main/java/com/stripe/param/FeeRefundUpdateParams.java
@@ -14,6 +14,15 @@ public class FeeRefundUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -22,8 +31,10 @@ public class FeeRefundUpdateParams extends ApiRequestParams {
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private FeeRefundUpdateParams(List<String> expand, Map<String, String> metadata) {
+  private FeeRefundUpdateParams(
+      List<String> expand, Map<String, Object> extraParams, Map<String, String> metadata) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -34,11 +45,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public FeeRefundUpdateParams build() {
-      return new FeeRefundUpdateParams(this.expand, this.metadata);
+      return new FeeRefundUpdateParams(this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -67,6 +80,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * FeeRefundUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link FeeRefundUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/FileLinkCreateParams.java b/src/main/java/com/stripe/param/FileLinkCreateParams.java
index 2d8e476b719..9b89145ed29 100644
--- a/src/main/java/com/stripe/param/FileLinkCreateParams.java
+++ b/src/main/java/com/stripe/param/FileLinkCreateParams.java
@@ -18,6 +18,15 @@ public class FileLinkCreateParams extends ApiRequestParams {
   @SerializedName("expires_at")
   Long expiresAt;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * The ID of the file. The file's `purpose` must be one of the following: `business_icon`,
    * `business_logo`, `customer_signature`, `dispute_evidence`, `finance_report_run`,
@@ -34,9 +43,14 @@ public class FileLinkCreateParams extends ApiRequestParams {
   Map<String, String> metadata;
 
   private FileLinkCreateParams(
-      List<String> expand, Long expiresAt, String file, Map<String, String> metadata) {
+      List<String> expand,
+      Long expiresAt,
+      Map<String, Object> extraParams,
+      String file,
+      Map<String, String> metadata) {
     this.expand = expand;
     this.expiresAt = expiresAt;
+    this.extraParams = extraParams;
     this.file = file;
     this.metadata = metadata;
   }
@@ -50,13 +64,16 @@ public static class Builder {
 
     private Long expiresAt;
 
+    private Map<String, Object> extraParams;
+
     private String file;
 
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public FileLinkCreateParams build() {
-      return new FileLinkCreateParams(this.expand, this.expiresAt, this.file, this.metadata);
+      return new FileLinkCreateParams(
+          this.expand, this.expiresAt, this.extraParams, this.file, this.metadata);
     }
 
     /**
@@ -91,6 +108,32 @@ public Builder setExpiresAt(Long expiresAt) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * FileLinkCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link FileLinkCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * The ID of the file. The file's `purpose` must be one of the following: `business_icon`,
      * `business_logo`, `customer_signature`, `dispute_evidence`, `finance_report_run`,
diff --git a/src/main/java/com/stripe/param/FileLinkListParams.java b/src/main/java/com/stripe/param/FileLinkListParams.java
index 109aee4c6ab..03ebf8dbae8 100644
--- a/src/main/java/com/stripe/param/FileLinkListParams.java
+++ b/src/main/java/com/stripe/param/FileLinkListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class FileLinkListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -28,6 +30,15 @@ public class FileLinkListParams extends ApiRequestParams {
   @SerializedName("expired")
   Boolean expired;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Only return links for the given file. */
   @SerializedName("file")
   String file;
@@ -53,6 +64,7 @@ private FileLinkListParams(
       String endingBefore,
       List<String> expand,
       Boolean expired,
+      Map<String, Object> extraParams,
       String file,
       Long limit,
       String startingAfter) {
@@ -60,6 +72,7 @@ private FileLinkListParams(
     this.endingBefore = endingBefore;
     this.expand = expand;
     this.expired = expired;
+    this.extraParams = extraParams;
     this.file = file;
     this.limit = limit;
     this.startingAfter = startingAfter;
@@ -78,6 +91,8 @@ public static class Builder {
 
     private Boolean expired;
 
+    private Map<String, Object> extraParams;
+
     private String file;
 
     private Long limit;
@@ -91,6 +106,7 @@ public FileLinkListParams build() {
           this.endingBefore,
           this.expand,
           this.expired,
+          this.extraParams,
           this.file,
           this.limit,
           this.startingAfter);
@@ -149,6 +165,32 @@ public Builder setExpired(Boolean expired) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * FileLinkListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link FileLinkListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Only return links for the given file. */
     public Builder setFile(String file) {
       this.file = file;
@@ -177,6 +219,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -193,7 +244,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -205,6 +257,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -215,7 +269,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * FileLinkListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link FileLinkListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/FileLinkRetrieveParams.java b/src/main/java/com/stripe/param/FileLinkRetrieveParams.java
index 6333784544b..a3811be6f4a 100644
--- a/src/main/java/com/stripe/param/FileLinkRetrieveParams.java
+++ b/src/main/java/com/stripe/param/FileLinkRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class FileLinkRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private FileLinkRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private FileLinkRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public FileLinkRetrieveParams build() {
-      return new FileLinkRetrieveParams(this.expand);
+      return new FileLinkRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * FileLinkRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link FileLinkRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/FileLinkUpdateParams.java b/src/main/java/com/stripe/param/FileLinkUpdateParams.java
index 439806c09a0..6e811e8d833 100644
--- a/src/main/java/com/stripe/param/FileLinkUpdateParams.java
+++ b/src/main/java/com/stripe/param/FileLinkUpdateParams.java
@@ -23,6 +23,15 @@ public class FileLinkUpdateParams extends ApiRequestParams {
   @SerializedName("expires_at")
   Object expiresAt;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -31,9 +40,13 @@ public class FileLinkUpdateParams extends ApiRequestParams {
   Map<String, String> metadata;
 
   private FileLinkUpdateParams(
-      List<String> expand, Object expiresAt, Map<String, String> metadata) {
+      List<String> expand,
+      Object expiresAt,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata) {
     this.expand = expand;
     this.expiresAt = expiresAt;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -46,11 +59,13 @@ public static class Builder {
 
     private Object expiresAt;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public FileLinkUpdateParams build() {
-      return new FileLinkUpdateParams(this.expand, this.expiresAt, this.metadata);
+      return new FileLinkUpdateParams(this.expand, this.expiresAt, this.extraParams, this.metadata);
     }
 
     /**
@@ -106,6 +121,32 @@ public Builder setExpiresAt(Long expiresAt) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * FileLinkUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link FileLinkUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/InvoiceCreateParams.java b/src/main/java/com/stripe/param/InvoiceCreateParams.java
index fa948af5ea7..4d63ec40753 100644
--- a/src/main/java/com/stripe/param/InvoiceCreateParams.java
+++ b/src/main/java/com/stripe/param/InvoiceCreateParams.java
@@ -86,6 +86,15 @@ public class InvoiceCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Footer to be displayed on the invoice. */
   @SerializedName("footer")
   String footer;
@@ -140,6 +149,7 @@ private InvoiceCreateParams(
       String description,
       Long dueDate,
       List<String> expand,
+      Map<String, Object> extraParams,
       String footer,
       Map<String, String> metadata,
       String statementDescriptor,
@@ -158,6 +168,7 @@ private InvoiceCreateParams(
     this.description = description;
     this.dueDate = dueDate;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.footer = footer;
     this.metadata = metadata;
     this.statementDescriptor = statementDescriptor;
@@ -195,6 +206,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String footer;
 
     private Map<String, String> metadata;
@@ -222,6 +235,7 @@ public InvoiceCreateParams build() {
           this.description,
           this.dueDate,
           this.expand,
+          this.extraParams,
           this.footer,
           this.metadata,
           this.statementDescriptor,
@@ -374,6 +388,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Footer to be displayed on the invoice. */
     public Builder setFooter(String footer) {
       this.footer = footer;
@@ -450,6 +490,15 @@ public Builder setTransferData(TransferData transferData) {
   }
 
   public static class CustomField {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The name of the custom field. This may be up to 30 characters. */
     @SerializedName("name")
     String name;
@@ -458,7 +507,8 @@ public static class CustomField {
     @SerializedName("value")
     String value;
 
-    private CustomField(String name, String value) {
+    private CustomField(Map<String, Object> extraParams, String name, String value) {
+      this.extraParams = extraParams;
       this.name = name;
       this.value = value;
     }
@@ -468,13 +518,41 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String value;
 
       /** Finalize and obtain parameter instance from this builder. */
       public CustomField build() {
-        return new CustomField(this.name, this.value);
+        return new CustomField(this.extraParams, this.name, this.value);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceCreateParams.CustomField#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceCreateParams.CustomField#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** The name of the custom field. This may be up to 30 characters. */
@@ -496,8 +574,18 @@ public static class TransferData {
     @SerializedName("destination")
     String destination;
 
-    private TransferData(String destination) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private TransferData(String destination, Map<String, Object> extraParams) {
       this.destination = destination;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -507,9 +595,11 @@ public static Builder builder() {
     public static class Builder {
       private String destination;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public TransferData build() {
-        return new TransferData(this.destination);
+        return new TransferData(this.destination, this.extraParams);
       }
 
       /** ID of an existing, connected Stripe account. */
@@ -517,6 +607,32 @@ public Builder setDestination(String destination) {
         this.destination = destination;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceCreateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceCreateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 
diff --git a/src/main/java/com/stripe/param/InvoiceFinalizeInvoiceParams.java b/src/main/java/com/stripe/param/InvoiceFinalizeInvoiceParams.java
index 336a2129f21..8146f834302 100644
--- a/src/main/java/com/stripe/param/InvoiceFinalizeInvoiceParams.java
+++ b/src/main/java/com/stripe/param/InvoiceFinalizeInvoiceParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoiceFinalizeInvoiceParams extends ApiRequestParams {
   /**
@@ -20,9 +22,20 @@ public class InvoiceFinalizeInvoiceParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
-  private InvoiceFinalizeInvoiceParams(Boolean autoAdvance, List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private InvoiceFinalizeInvoiceParams(
+      Boolean autoAdvance, List<String> expand, Map<String, Object> extraParams) {
     this.autoAdvance = autoAdvance;
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -34,9 +47,11 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public InvoiceFinalizeInvoiceParams build() {
-      return new InvoiceFinalizeInvoiceParams(this.autoAdvance, this.expand);
+      return new InvoiceFinalizeInvoiceParams(this.autoAdvance, this.expand, this.extraParams);
     }
 
     /**
@@ -74,5 +89,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceFinalizeInvoiceParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceFinalizeInvoiceParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/InvoiceItemCreateParams.java b/src/main/java/com/stripe/param/InvoiceItemCreateParams.java
index 9a9fa3a08ac..18b7d89f648 100644
--- a/src/main/java/com/stripe/param/InvoiceItemCreateParams.java
+++ b/src/main/java/com/stripe/param/InvoiceItemCreateParams.java
@@ -46,6 +46,15 @@ public class InvoiceItemCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * The ID of an existing invoice to add this invoice item to. When left blank, the invoice item
    * will be added to the next upcoming scheduled invoice. This is useful when adding invoice items
@@ -100,6 +109,7 @@ private InvoiceItemCreateParams(
       String description,
       Boolean discountable,
       List<String> expand,
+      Map<String, Object> extraParams,
       String invoice,
       Map<String, String> metadata,
       Period period,
@@ -113,6 +123,7 @@ private InvoiceItemCreateParams(
     this.description = description;
     this.discountable = discountable;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoice = invoice;
     this.metadata = metadata;
     this.period = period;
@@ -139,6 +150,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String invoice;
 
     private Map<String, String> metadata;
@@ -162,6 +175,7 @@ public InvoiceItemCreateParams build() {
           this.description,
           this.discountable,
           this.expand,
+          this.extraParams,
           this.invoice,
           this.metadata,
           this.period,
@@ -239,6 +253,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceItemCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceItemCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * The ID of an existing invoice to add this invoice item to. When left blank, the invoice item
      * will be added to the next upcoming scheduled invoice. This is useful when adding invoice
@@ -342,12 +382,22 @@ public static class Period {
     @SerializedName("end")
     Long end;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The start of the period. */
     @SerializedName("start")
     Long start;
 
-    private Period(Long end, Long start) {
+    private Period(Long end, Map<String, Object> extraParams, Long start) {
       this.end = end;
+      this.extraParams = extraParams;
       this.start = start;
     }
 
@@ -358,11 +408,13 @@ public static Builder builder() {
     public static class Builder {
       private Long end;
 
+      private Map<String, Object> extraParams;
+
       private Long start;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Period build() {
-        return new Period(this.end, this.start);
+        return new Period(this.end, this.extraParams, this.start);
       }
 
       /** The end of the period, which must be greater than or equal to the start. */
@@ -371,6 +423,32 @@ public Builder setEnd(Long end) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceItemCreateParams.Period#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceItemCreateParams.Period#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The start of the period. */
       public Builder setStart(Long start) {
         this.start = start;
diff --git a/src/main/java/com/stripe/param/InvoiceItemListParams.java b/src/main/java/com/stripe/param/InvoiceItemListParams.java
index 557cf7f0753..ca76b350ad9 100644
--- a/src/main/java/com/stripe/param/InvoiceItemListParams.java
+++ b/src/main/java/com/stripe/param/InvoiceItemListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoiceItemListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -31,6 +33,15 @@ public class InvoiceItemListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Only return invoice items belonging to this invoice. If none is provided, all invoice items
    * will be returned. If specifying an invoice, no customer identifier is needed.
@@ -67,6 +78,7 @@ private InvoiceItemListParams(
       String customer,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       String invoice,
       Long limit,
       Boolean pending,
@@ -75,6 +87,7 @@ private InvoiceItemListParams(
     this.customer = customer;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoice = invoice;
     this.limit = limit;
     this.pending = pending;
@@ -94,6 +107,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String invoice;
 
     private Long limit;
@@ -109,6 +124,7 @@ public InvoiceItemListParams build() {
           this.customer,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.invoice,
           this.limit,
           this.pending,
@@ -171,6 +187,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceItemListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceItemListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Only return invoice items belonging to this invoice. If none is provided, all invoice items
      * will be returned. If specifying an invoice, no customer identifier is needed.
@@ -212,6 +254,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -228,7 +279,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -240,6 +292,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -250,7 +304,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceItemListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceItemListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/InvoiceItemRetrieveParams.java b/src/main/java/com/stripe/param/InvoiceItemRetrieveParams.java
index 1094ea96538..0da9c13fe1f 100644
--- a/src/main/java/com/stripe/param/InvoiceItemRetrieveParams.java
+++ b/src/main/java/com/stripe/param/InvoiceItemRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoiceItemRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private InvoiceItemRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private InvoiceItemRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public InvoiceItemRetrieveParams build() {
-      return new InvoiceItemRetrieveParams(this.expand);
+      return new InvoiceItemRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceItemRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceItemRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/InvoiceItemUpdateParams.java b/src/main/java/com/stripe/param/InvoiceItemUpdateParams.java
index c7a8c8ae782..3a7286ec9f1 100644
--- a/src/main/java/com/stripe/param/InvoiceItemUpdateParams.java
+++ b/src/main/java/com/stripe/param/InvoiceItemUpdateParams.java
@@ -37,6 +37,15 @@ public class InvoiceItemUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to an invoice item object. It can be useful for
    * storing additional information about the invoice item in a structured format.
@@ -72,6 +81,7 @@ private InvoiceItemUpdateParams(
       String description,
       Boolean discountable,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       Period period,
       Long quantity,
@@ -81,6 +91,7 @@ private InvoiceItemUpdateParams(
     this.description = description;
     this.discountable = discountable;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.period = period;
     this.quantity = quantity;
@@ -101,6 +112,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private Period period;
@@ -118,6 +131,7 @@ public InvoiceItemUpdateParams build() {
           this.description,
           this.discountable,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.period,
           this.quantity,
@@ -179,6 +193,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceItemUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceItemUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -251,12 +291,22 @@ public static class Period {
     @SerializedName("end")
     Long end;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The start of the period. */
     @SerializedName("start")
     Long start;
 
-    private Period(Long end, Long start) {
+    private Period(Long end, Map<String, Object> extraParams, Long start) {
       this.end = end;
+      this.extraParams = extraParams;
       this.start = start;
     }
 
@@ -267,11 +317,13 @@ public static Builder builder() {
     public static class Builder {
       private Long end;
 
+      private Map<String, Object> extraParams;
+
       private Long start;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Period build() {
-        return new Period(this.end, this.start);
+        return new Period(this.end, this.extraParams, this.start);
       }
 
       /** The end of the period, which must be greater than or equal to the start. */
@@ -280,6 +332,32 @@ public Builder setEnd(Long end) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceItemUpdateParams.Period#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceItemUpdateParams.Period#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The start of the period. */
       public Builder setStart(Long start) {
         this.start = start;
diff --git a/src/main/java/com/stripe/param/InvoiceLineItemCollectionListParams.java b/src/main/java/com/stripe/param/InvoiceLineItemCollectionListParams.java
index 90cc34f45cd..84611733580 100644
--- a/src/main/java/com/stripe/param/InvoiceLineItemCollectionListParams.java
+++ b/src/main/java/com/stripe/param/InvoiceLineItemCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoiceLineItemCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class InvoiceLineItemCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class InvoiceLineItemCollectionListParams extends ApiRequestParams {
   String startingAfter;
 
   private InvoiceLineItemCollectionListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public InvoiceLineItemCollectionListParams build() {
       return new InvoiceLineItemCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceLineItemCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceLineItemCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/InvoiceListParams.java b/src/main/java/com/stripe/param/InvoiceListParams.java
index 00a152cddb2..c9654cd5312 100644
--- a/src/main/java/com/stripe/param/InvoiceListParams.java
+++ b/src/main/java/com/stripe/param/InvoiceListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class InvoiceListParams extends ApiRequestParams {
@@ -38,6 +40,15 @@ public class InvoiceListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -65,6 +76,7 @@ private InvoiceListParams(
       Object dueDate,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       String subscription) {
@@ -74,6 +86,7 @@ private InvoiceListParams(
     this.dueDate = dueDate;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.subscription = subscription;
@@ -96,6 +109,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -111,6 +126,7 @@ public InvoiceListParams build() {
           this.dueDate,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter,
           this.subscription);
@@ -187,6 +203,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -215,6 +257,15 @@ public Builder setSubscription(String subscription) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -231,7 +282,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -243,6 +295,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -253,7 +307,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -283,6 +363,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class DueDate {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -299,7 +388,8 @@ public static class DueDate {
     @SerializedName("lte")
     Long lte;
 
-    private DueDate(Long gt, Long gte, Long lt, Long lte) {
+    private DueDate(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -311,6 +401,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -321,7 +413,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public DueDate build() {
-        return new DueDate(this.gt, this.gte, this.lt, this.lte);
+        return new DueDate(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceListParams.DueDate#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceListParams.DueDate#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/InvoiceMarkUncollectibleParams.java b/src/main/java/com/stripe/param/InvoiceMarkUncollectibleParams.java
index 1e26218bb9d..3c161c2c2c0 100644
--- a/src/main/java/com/stripe/param/InvoiceMarkUncollectibleParams.java
+++ b/src/main/java/com/stripe/param/InvoiceMarkUncollectibleParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoiceMarkUncollectibleParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private InvoiceMarkUncollectibleParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private InvoiceMarkUncollectibleParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public InvoiceMarkUncollectibleParams build() {
-      return new InvoiceMarkUncollectibleParams(this.expand);
+      return new InvoiceMarkUncollectibleParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceMarkUncollectibleParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceMarkUncollectibleParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/InvoicePayParams.java b/src/main/java/com/stripe/param/InvoicePayParams.java
index 5ba3585506a..b89cc8e56b0 100644
--- a/src/main/java/com/stripe/param/InvoicePayParams.java
+++ b/src/main/java/com/stripe/param/InvoicePayParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoicePayParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * In cases where the source used to pay the invoice has insufficient funds, passing
    * `forgive=true` controls whether a charge should be attempted for the full amount available on
@@ -48,11 +59,13 @@ public class InvoicePayParams extends ApiRequestParams {
 
   private InvoicePayParams(
       List<String> expand,
+      Map<String, Object> extraParams,
       Boolean forgive,
       Boolean paidOutOfBand,
       String paymentMethod,
       String source) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.forgive = forgive;
     this.paidOutOfBand = paidOutOfBand;
     this.paymentMethod = paymentMethod;
@@ -66,6 +79,8 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean forgive;
 
     private Boolean paidOutOfBand;
@@ -77,7 +92,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public InvoicePayParams build() {
       return new InvoicePayParams(
-          this.expand, this.forgive, this.paidOutOfBand, this.paymentMethod, this.source);
+          this.expand,
+          this.extraParams,
+          this.forgive,
+          this.paidOutOfBand,
+          this.paymentMethod,
+          this.source);
     }
 
     /**
@@ -106,6 +126,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoicePayParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoicePayParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * In cases where the source used to pay the invoice has insufficient funds, passing
      * `forgive=true` controls whether a charge should be attempted for the full amount available on
diff --git a/src/main/java/com/stripe/param/InvoiceRetrieveParams.java b/src/main/java/com/stripe/param/InvoiceRetrieveParams.java
index e1cebdce24e..2fdfdb7411a 100644
--- a/src/main/java/com/stripe/param/InvoiceRetrieveParams.java
+++ b/src/main/java/com/stripe/param/InvoiceRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoiceRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private InvoiceRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private InvoiceRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public InvoiceRetrieveParams build() {
-      return new InvoiceRetrieveParams(this.expand);
+      return new InvoiceRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/InvoiceSendInvoiceParams.java b/src/main/java/com/stripe/param/InvoiceSendInvoiceParams.java
index 3024e25fc94..bd947abb858 100644
--- a/src/main/java/com/stripe/param/InvoiceSendInvoiceParams.java
+++ b/src/main/java/com/stripe/param/InvoiceSendInvoiceParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoiceSendInvoiceParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private InvoiceSendInvoiceParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private InvoiceSendInvoiceParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public InvoiceSendInvoiceParams build() {
-      return new InvoiceSendInvoiceParams(this.expand);
+      return new InvoiceSendInvoiceParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceSendInvoiceParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceSendInvoiceParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/InvoiceUpcomingParams.java b/src/main/java/com/stripe/param/InvoiceUpcomingParams.java
index 9bd63408808..a9eb4d90f66 100644
--- a/src/main/java/com/stripe/param/InvoiceUpcomingParams.java
+++ b/src/main/java/com/stripe/param/InvoiceUpcomingParams.java
@@ -31,6 +31,15 @@ public class InvoiceUpcomingParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** List of invoice items to add or update in the upcoming invoice preview. */
   @SerializedName("invoice_items")
   List<InvoiceItem> invoiceItems;
@@ -115,6 +124,7 @@ private InvoiceUpcomingParams(
       String coupon,
       String customer,
       List<String> expand,
+      Map<String, Object> extraParams,
       List<InvoiceItem> invoiceItems,
       String subscription,
       Object subscriptionBillingCycleAnchor,
@@ -130,6 +140,7 @@ private InvoiceUpcomingParams(
     this.coupon = coupon;
     this.customer = customer;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoiceItems = invoiceItems;
     this.subscription = subscription;
     this.subscriptionBillingCycleAnchor = subscriptionBillingCycleAnchor;
@@ -155,6 +166,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<InvoiceItem> invoiceItems;
 
     private String subscription;
@@ -185,6 +198,7 @@ public InvoiceUpcomingParams build() {
           this.coupon,
           this.customer,
           this.expand,
+          this.extraParams,
           this.invoiceItems,
           this.subscription,
           this.subscriptionBillingCycleAnchor,
@@ -243,6 +257,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceUpcomingParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceUpcomingParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `invoiceItems` list. A list is initialized for the first `add/addAll` call,
      * and subsequent calls adds additional elements to the original list. See {@link
@@ -443,6 +483,15 @@ public static class InvoiceItem {
     @SerializedName("discountable")
     Boolean discountable;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The ID of the invoice item to update in preview. If not specified, a new invoice item will be
      * added to the preview of the upcoming invoice.
@@ -481,6 +530,7 @@ private InvoiceItem(
         String currency,
         String description,
         Boolean discountable,
+        Map<String, Object> extraParams,
         String invoiceitem,
         Map<String, String> metadata,
         Period period,
@@ -491,6 +541,7 @@ private InvoiceItem(
       this.currency = currency;
       this.description = description;
       this.discountable = discountable;
+      this.extraParams = extraParams;
       this.invoiceitem = invoiceitem;
       this.metadata = metadata;
       this.period = period;
@@ -512,6 +563,8 @@ public static class Builder {
 
       private Boolean discountable;
 
+      private Map<String, Object> extraParams;
+
       private String invoiceitem;
 
       private Map<String, String> metadata;
@@ -531,6 +584,7 @@ public InvoiceItem build() {
             this.currency,
             this.description,
             this.discountable,
+            this.extraParams,
             this.invoiceitem,
             this.metadata,
             this.period,
@@ -573,6 +627,32 @@ public Builder setDiscountable(Boolean discountable) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceUpcomingParams.InvoiceItem#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceUpcomingParams.InvoiceItem#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * The ID of the invoice item to update in preview. If not specified, a new invoice item will
        * be added to the preview of the upcoming invoice.
@@ -646,12 +726,22 @@ public static class Period {
       @SerializedName("end")
       Long end;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** The start of the period. */
       @SerializedName("start")
       Long start;
 
-      private Period(Long end, Long start) {
+      private Period(Long end, Map<String, Object> extraParams, Long start) {
         this.end = end;
+        this.extraParams = extraParams;
         this.start = start;
       }
 
@@ -662,11 +752,13 @@ public static Builder builder() {
       public static class Builder {
         private Long end;
 
+        private Map<String, Object> extraParams;
+
         private Long start;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Period build() {
-          return new Period(this.end, this.start);
+          return new Period(this.end, this.extraParams, this.start);
         }
 
         /** The end of the period, which must be greater than or equal to the start. */
@@ -675,6 +767,34 @@ public Builder setEnd(Long end) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link InvoiceUpcomingParams.InvoiceItem.Period#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link InvoiceUpcomingParams.InvoiceItem.Period#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** The start of the period. */
         public Builder setStart(Long start) {
           this.start = start;
@@ -703,6 +823,15 @@ public static class SubscriptionItem {
     @SerializedName("deleted")
     Boolean deleted;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Subscription item to update. */
     @SerializedName("id")
     String id;
@@ -733,6 +862,7 @@ private SubscriptionItem(
         Object billingThresholds,
         Boolean clearUsage,
         Boolean deleted,
+        Map<String, Object> extraParams,
         String id,
         Map<String, String> metadata,
         String plan,
@@ -741,6 +871,7 @@ private SubscriptionItem(
       this.billingThresholds = billingThresholds;
       this.clearUsage = clearUsage;
       this.deleted = deleted;
+      this.extraParams = extraParams;
       this.id = id;
       this.metadata = metadata;
       this.plan = plan;
@@ -759,6 +890,8 @@ public static class Builder {
 
       private Boolean deleted;
 
+      private Map<String, Object> extraParams;
+
       private String id;
 
       private Map<String, String> metadata;
@@ -775,6 +908,7 @@ public SubscriptionItem build() {
             this.billingThresholds,
             this.clearUsage,
             this.deleted,
+            this.extraParams,
             this.id,
             this.metadata,
             this.plan,
@@ -815,6 +949,32 @@ public Builder setDeleted(Boolean deleted) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceUpcomingParams.SubscriptionItem#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceUpcomingParams.SubscriptionItem#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Subscription item to update. */
       public Builder setId(String id) {
         this.id = id;
@@ -879,11 +1039,21 @@ public Builder setTaxRates(List<String> taxRates) {
     }
 
     public static class BillingThresholds {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Usage threshold that triggers the subscription to advance to a new billing period. */
       @SerializedName("usage_gte")
       Long usageGte;
 
-      private BillingThresholds(Long usageGte) {
+      private BillingThresholds(Map<String, Object> extraParams, Long usageGte) {
+        this.extraParams = extraParams;
         this.usageGte = usageGte;
       }
 
@@ -893,11 +1063,41 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private Long usageGte;
 
         /** Finalize and obtain parameter instance from this builder. */
         public BillingThresholds build() {
-          return new BillingThresholds(this.usageGte);
+          return new BillingThresholds(this.extraParams, this.usageGte);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link InvoiceUpcomingParams.SubscriptionItem.BillingThresholds#extraParams} for
+         * the field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link InvoiceUpcomingParams.SubscriptionItem.BillingThresholds#extraParams} for
+         * the field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** Usage threshold that triggers the subscription to advance to a new billing period. */
diff --git a/src/main/java/com/stripe/param/InvoiceUpdateParams.java b/src/main/java/com/stripe/param/InvoiceUpdateParams.java
index 92b227c7974..b9a1e1ba672 100644
--- a/src/main/java/com/stripe/param/InvoiceUpdateParams.java
+++ b/src/main/java/com/stripe/param/InvoiceUpdateParams.java
@@ -75,6 +75,15 @@ public class InvoiceUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Footer to be displayed on the invoice. */
   @SerializedName("footer")
   String footer;
@@ -120,6 +129,7 @@ private InvoiceUpdateParams(
       String description,
       Long dueDate,
       List<String> expand,
+      Map<String, Object> extraParams,
       String footer,
       Map<String, String> metadata,
       String statementDescriptor,
@@ -135,6 +145,7 @@ private InvoiceUpdateParams(
     this.description = description;
     this.dueDate = dueDate;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.footer = footer;
     this.metadata = metadata;
     this.statementDescriptor = statementDescriptor;
@@ -167,6 +178,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String footer;
 
     private Map<String, String> metadata;
@@ -190,6 +203,7 @@ public InvoiceUpdateParams build() {
           this.description,
           this.dueDate,
           this.expand,
+          this.extraParams,
           this.footer,
           this.metadata,
           this.statementDescriptor,
@@ -316,6 +330,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Footer to be displayed on the invoice. */
     public Builder setFooter(String footer) {
       this.footer = footer;
@@ -405,6 +445,15 @@ public Builder setTransferData(EmptyParam transferData) {
   }
 
   public static class CustomField {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The name of the custom field. This may be up to 30 characters. */
     @SerializedName("name")
     String name;
@@ -413,7 +462,8 @@ public static class CustomField {
     @SerializedName("value")
     String value;
 
-    private CustomField(String name, String value) {
+    private CustomField(Map<String, Object> extraParams, String name, String value) {
+      this.extraParams = extraParams;
       this.name = name;
       this.value = value;
     }
@@ -423,13 +473,41 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String value;
 
       /** Finalize and obtain parameter instance from this builder. */
       public CustomField build() {
-        return new CustomField(this.name, this.value);
+        return new CustomField(this.extraParams, this.name, this.value);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceUpdateParams.CustomField#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceUpdateParams.CustomField#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** The name of the custom field. This may be up to 30 characters. */
@@ -451,8 +529,18 @@ public static class TransferData {
     @SerializedName("destination")
     String destination;
 
-    private TransferData(String destination) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private TransferData(String destination, Map<String, Object> extraParams) {
       this.destination = destination;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -462,9 +550,11 @@ public static Builder builder() {
     public static class Builder {
       private String destination;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public TransferData build() {
-        return new TransferData(this.destination);
+        return new TransferData(this.destination, this.extraParams);
       }
 
       /** ID of an existing, connected Stripe account. */
@@ -472,6 +562,32 @@ public Builder setDestination(String destination) {
         this.destination = destination;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * InvoiceUpdateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link InvoiceUpdateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 }
diff --git a/src/main/java/com/stripe/param/InvoiceVoidInvoiceParams.java b/src/main/java/com/stripe/param/InvoiceVoidInvoiceParams.java
index 142d0d0fb44..d77e689be56 100644
--- a/src/main/java/com/stripe/param/InvoiceVoidInvoiceParams.java
+++ b/src/main/java/com/stripe/param/InvoiceVoidInvoiceParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class InvoiceVoidInvoiceParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private InvoiceVoidInvoiceParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private InvoiceVoidInvoiceParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public InvoiceVoidInvoiceParams build() {
-      return new InvoiceVoidInvoiceParams(this.expand);
+      return new InvoiceVoidInvoiceParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * InvoiceVoidInvoiceParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link InvoiceVoidInvoiceParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/IssuerFraudRecordListParams.java b/src/main/java/com/stripe/param/IssuerFraudRecordListParams.java
index 858244a2c6a..a4cd237cae1 100644
--- a/src/main/java/com/stripe/param/IssuerFraudRecordListParams.java
+++ b/src/main/java/com/stripe/param/IssuerFraudRecordListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class IssuerFraudRecordListParams extends ApiRequestParams {
   /** Only return issuer fraud records for the charge specified by this charge ID. */
@@ -25,6 +27,15 @@ public class IssuerFraudRecordListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -42,10 +53,16 @@ public class IssuerFraudRecordListParams extends ApiRequestParams {
   String startingAfter;
 
   private IssuerFraudRecordListParams(
-      String charge, String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String charge,
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.charge = charge;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -61,6 +78,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -68,7 +87,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public IssuerFraudRecordListParams build() {
       return new IssuerFraudRecordListParams(
-          this.charge, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.charge,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     /** Only return issuer fraud records for the charge specified by this charge ID. */
@@ -114,6 +138,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * IssuerFraudRecordListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link IssuerFraudRecordListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/IssuerFraudRecordRetrieveParams.java b/src/main/java/com/stripe/param/IssuerFraudRecordRetrieveParams.java
index c9c80e45159..9e92f13c51e 100644
--- a/src/main/java/com/stripe/param/IssuerFraudRecordRetrieveParams.java
+++ b/src/main/java/com/stripe/param/IssuerFraudRecordRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class IssuerFraudRecordRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private IssuerFraudRecordRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private IssuerFraudRecordRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public IssuerFraudRecordRetrieveParams build() {
-      return new IssuerFraudRecordRetrieveParams(this.expand);
+      return new IssuerFraudRecordRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * IssuerFraudRecordRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link IssuerFraudRecordRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/LoginLinkCreateOnAccountParams.java b/src/main/java/com/stripe/param/LoginLinkCreateOnAccountParams.java
index 2612503bfb6..46790adf185 100644
--- a/src/main/java/com/stripe/param/LoginLinkCreateOnAccountParams.java
+++ b/src/main/java/com/stripe/param/LoginLinkCreateOnAccountParams.java
@@ -5,19 +5,32 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class LoginLinkCreateOnAccountParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Where to redirect the user after they log out of their dashboard. */
   @SerializedName("redirect_url")
   String redirectUrl;
 
-  private LoginLinkCreateOnAccountParams(List<String> expand, String redirectUrl) {
+  private LoginLinkCreateOnAccountParams(
+      List<String> expand, Map<String, Object> extraParams, String redirectUrl) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.redirectUrl = redirectUrl;
   }
 
@@ -28,11 +41,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String redirectUrl;
 
     /** Finalize and obtain parameter instance from this builder. */
     public LoginLinkCreateOnAccountParams build() {
-      return new LoginLinkCreateOnAccountParams(this.expand, this.redirectUrl);
+      return new LoginLinkCreateOnAccountParams(this.expand, this.extraParams, this.redirectUrl);
     }
 
     /**
@@ -61,6 +76,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * LoginLinkCreateOnAccountParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link LoginLinkCreateOnAccountParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Where to redirect the user after they log out of their dashboard. */
     public Builder setRedirectUrl(String redirectUrl) {
       this.redirectUrl = redirectUrl;
diff --git a/src/main/java/com/stripe/param/OrderCreateParams.java b/src/main/java/com/stripe/param/OrderCreateParams.java
index b919abb9d5c..91a4d778273 100644
--- a/src/main/java/com/stripe/param/OrderCreateParams.java
+++ b/src/main/java/com/stripe/param/OrderCreateParams.java
@@ -42,6 +42,15 @@ public class OrderCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** List of items constituting the order. An order can have up to 25 items. */
   @SerializedName("items")
   List<Item> items;
@@ -67,6 +76,7 @@ private OrderCreateParams(
       String customer,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       List<Item> items,
       Map<String, String> metadata,
       Shipping shipping) {
@@ -75,6 +85,7 @@ private OrderCreateParams(
     this.customer = customer;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.items = items;
     this.metadata = metadata;
     this.shipping = shipping;
@@ -95,6 +106,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<Item> items;
 
     private Map<String, String> metadata;
@@ -109,6 +122,7 @@ public OrderCreateParams build() {
           this.customer,
           this.email,
           this.expand,
+          this.extraParams,
           this.items,
           this.metadata,
           this.shipping);
@@ -175,6 +189,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * OrderCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link OrderCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `items` list. A list is initialized for the first `add/addAll` call, and
      * subsequent calls adds additional elements to the original list. See {@link
@@ -247,6 +287,15 @@ public static class Item {
     @SerializedName("description")
     String description;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The ID of the SKU being ordered. */
     @SerializedName("parent")
     String parent;
@@ -262,10 +311,17 @@ public static class Item {
     Type type;
 
     private Item(
-        Long amount, String currency, String description, String parent, Long quantity, Type type) {
+        Long amount,
+        String currency,
+        String description,
+        Map<String, Object> extraParams,
+        String parent,
+        Long quantity,
+        Type type) {
       this.amount = amount;
       this.currency = currency;
       this.description = description;
+      this.extraParams = extraParams;
       this.parent = parent;
       this.quantity = quantity;
       this.type = type;
@@ -282,6 +338,8 @@ public static class Builder {
 
       private String description;
 
+      private Map<String, Object> extraParams;
+
       private String parent;
 
       private Long quantity;
@@ -291,7 +349,13 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Item build() {
         return new Item(
-            this.amount, this.currency, this.description, this.parent, this.quantity, this.type);
+            this.amount,
+            this.currency,
+            this.description,
+            this.extraParams,
+            this.parent,
+            this.quantity,
+            this.type);
       }
 
       public Builder setAmount(Long amount) {
@@ -309,6 +373,32 @@ public Builder setDescription(String description) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * OrderCreateParams.Item#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link OrderCreateParams.Item#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The ID of the SKU being ordered. */
       public Builder setParent(String parent) {
         this.parent = parent;
@@ -357,6 +447,15 @@ public static class Shipping {
     @SerializedName("address")
     Address address;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Customer name. */
     @SerializedName("name")
     String name;
@@ -365,8 +464,9 @@ public static class Shipping {
     @SerializedName("phone")
     String phone;
 
-    private Shipping(Address address, String name, String phone) {
+    private Shipping(Address address, Map<String, Object> extraParams, String name, String phone) {
       this.address = address;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
     }
@@ -378,13 +478,15 @@ public static Builder builder() {
     public static class Builder {
       private Address address;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.name, this.phone);
+        return new Shipping(this.address, this.extraParams, this.name, this.phone);
       }
 
       /** Customer shipping address. */
@@ -393,6 +495,32 @@ public Builder setAddress(Address address) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * OrderCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link OrderCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Customer name. */
       public Builder setName(String name) {
         this.name = name;
@@ -413,6 +541,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -428,12 +565,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -449,6 +588,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -460,7 +601,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -473,6 +620,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
diff --git a/src/main/java/com/stripe/param/OrderListParams.java b/src/main/java/com/stripe/param/OrderListParams.java
index 85119a324e5..98955d54bd5 100644
--- a/src/main/java/com/stripe/param/OrderListParams.java
+++ b/src/main/java/com/stripe/param/OrderListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class OrderListParams extends ApiRequestParams {
   /** Date this order was created. */
@@ -29,6 +31,15 @@ public class OrderListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Only return orders with the given IDs. */
   @SerializedName("ids")
   List<String> ids;
@@ -69,6 +80,7 @@ private OrderListParams(
       String customer,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       List<String> ids,
       Long limit,
       String startingAfter,
@@ -79,6 +91,7 @@ private OrderListParams(
     this.customer = customer;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.ids = ids;
     this.limit = limit;
     this.startingAfter = startingAfter;
@@ -100,6 +113,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<String> ids;
 
     private Long limit;
@@ -119,6 +134,7 @@ public OrderListParams build() {
           this.customer,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.ids,
           this.limit,
           this.startingAfter,
@@ -182,6 +198,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * OrderListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link OrderListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `ids` list. A list is initialized for the first `add/addAll` call, and
      * subsequent calls adds additional elements to the original list. See {@link
@@ -271,6 +313,15 @@ public Builder addAllUpstreamId(List<String> elements) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -287,7 +338,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -299,6 +351,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -309,7 +363,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * OrderListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link OrderListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -343,6 +423,15 @@ public static class StatusTransitions {
     @SerializedName("canceled")
     Object canceled;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Date this order was fulfilled. */
     @SerializedName("fulfilled")
     Object fulfilled;
@@ -355,8 +444,14 @@ public static class StatusTransitions {
     @SerializedName("returned")
     Object returned;
 
-    private StatusTransitions(Object canceled, Object fulfilled, Object paid, Object returned) {
+    private StatusTransitions(
+        Object canceled,
+        Map<String, Object> extraParams,
+        Object fulfilled,
+        Object paid,
+        Object returned) {
       this.canceled = canceled;
+      this.extraParams = extraParams;
       this.fulfilled = fulfilled;
       this.paid = paid;
       this.returned = returned;
@@ -369,6 +464,8 @@ public static Builder builder() {
     public static class Builder {
       private Object canceled;
 
+      private Map<String, Object> extraParams;
+
       private Object fulfilled;
 
       private Object paid;
@@ -377,7 +474,8 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public StatusTransitions build() {
-        return new StatusTransitions(this.canceled, this.fulfilled, this.paid, this.returned);
+        return new StatusTransitions(
+            this.canceled, this.extraParams, this.fulfilled, this.paid, this.returned);
       }
 
       /** Date this order was canceled. */
@@ -392,6 +490,32 @@ public Builder setCanceled(Long canceled) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * OrderListParams.StatusTransitions#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link OrderListParams.StatusTransitions#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Date this order was fulfilled. */
       public Builder setFulfilled(Fulfilled fulfilled) {
         this.fulfilled = fulfilled;
@@ -430,6 +554,15 @@ public Builder setReturned(Long returned) {
     }
 
     public static class Canceled {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Minimum value to filter by (exclusive). */
       @SerializedName("gt")
       Long gt;
@@ -446,7 +579,8 @@ public static class Canceled {
       @SerializedName("lte")
       Long lte;
 
-      private Canceled(Long gt, Long gte, Long lt, Long lte) {
+      private Canceled(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+        this.extraParams = extraParams;
         this.gt = gt;
         this.gte = gte;
         this.lt = lt;
@@ -458,6 +592,8 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private Long gt;
 
         private Long gte;
@@ -468,7 +604,35 @@ public static class Builder {
 
         /** Finalize and obtain parameter instance from this builder. */
         public Canceled build() {
-          return new Canceled(this.gt, this.gte, this.lt, this.lte);
+          return new Canceled(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderListParams.StatusTransitions.Canceled#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderListParams.StatusTransitions.Canceled#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** Minimum value to filter by (exclusive). */
@@ -498,6 +662,15 @@ public Builder setLte(Long lte) {
     }
 
     public static class Fulfilled {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Minimum value to filter by (exclusive). */
       @SerializedName("gt")
       Long gt;
@@ -514,7 +687,8 @@ public static class Fulfilled {
       @SerializedName("lte")
       Long lte;
 
-      private Fulfilled(Long gt, Long gte, Long lt, Long lte) {
+      private Fulfilled(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+        this.extraParams = extraParams;
         this.gt = gt;
         this.gte = gte;
         this.lt = lt;
@@ -526,6 +700,8 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private Long gt;
 
         private Long gte;
@@ -536,7 +712,35 @@ public static class Builder {
 
         /** Finalize and obtain parameter instance from this builder. */
         public Fulfilled build() {
-          return new Fulfilled(this.gt, this.gte, this.lt, this.lte);
+          return new Fulfilled(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderListParams.StatusTransitions.Fulfilled#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderListParams.StatusTransitions.Fulfilled#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** Minimum value to filter by (exclusive). */
@@ -566,6 +770,15 @@ public Builder setLte(Long lte) {
     }
 
     public static class Paid {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Minimum value to filter by (exclusive). */
       @SerializedName("gt")
       Long gt;
@@ -582,7 +795,8 @@ public static class Paid {
       @SerializedName("lte")
       Long lte;
 
-      private Paid(Long gt, Long gte, Long lt, Long lte) {
+      private Paid(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+        this.extraParams = extraParams;
         this.gt = gt;
         this.gte = gte;
         this.lt = lt;
@@ -594,6 +808,8 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private Long gt;
 
         private Long gte;
@@ -604,7 +820,35 @@ public static class Builder {
 
         /** Finalize and obtain parameter instance from this builder. */
         public Paid build() {
-          return new Paid(this.gt, this.gte, this.lt, this.lte);
+          return new Paid(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderListParams.StatusTransitions.Paid#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderListParams.StatusTransitions.Paid#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** Minimum value to filter by (exclusive). */
@@ -634,6 +878,15 @@ public Builder setLte(Long lte) {
     }
 
     public static class Returned {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Minimum value to filter by (exclusive). */
       @SerializedName("gt")
       Long gt;
@@ -650,7 +903,8 @@ public static class Returned {
       @SerializedName("lte")
       Long lte;
 
-      private Returned(Long gt, Long gte, Long lt, Long lte) {
+      private Returned(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+        this.extraParams = extraParams;
         this.gt = gt;
         this.gte = gte;
         this.lt = lt;
@@ -662,6 +916,8 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private Long gt;
 
         private Long gte;
@@ -672,7 +928,35 @@ public static class Builder {
 
         /** Finalize and obtain parameter instance from this builder. */
         public Returned build() {
-          return new Returned(this.gt, this.gte, this.lt, this.lte);
+          return new Returned(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderListParams.StatusTransitions.Returned#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link OrderListParams.StatusTransitions.Returned#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/OrderPayParams.java b/src/main/java/com/stripe/param/OrderPayParams.java
index a9321b754af..62b87b14c6f 100644
--- a/src/main/java/com/stripe/param/OrderPayParams.java
+++ b/src/main/java/com/stripe/param/OrderPayParams.java
@@ -32,6 +32,15 @@ public class OrderPayParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to an order object. Limited to 500 characters.
    * Metadata can be useful for storing additional information about the order in a structured
@@ -55,12 +64,14 @@ private OrderPayParams(
       String customer,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String source) {
     this.applicationFee = applicationFee;
     this.customer = customer;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.source = source;
   }
@@ -78,6 +89,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String source;
@@ -85,7 +98,13 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public OrderPayParams build() {
       return new OrderPayParams(
-          this.applicationFee, this.customer, this.email, this.expand, this.metadata, this.source);
+          this.applicationFee,
+          this.customer,
+          this.email,
+          this.expand,
+          this.extraParams,
+          this.metadata,
+          this.source);
     }
 
     public Builder setApplicationFee(Long applicationFee) {
@@ -138,6 +157,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * OrderPayParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link OrderPayParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/OrderRetrieveParams.java b/src/main/java/com/stripe/param/OrderRetrieveParams.java
index e8b93a0cf25..48a7be1f062 100644
--- a/src/main/java/com/stripe/param/OrderRetrieveParams.java
+++ b/src/main/java/com/stripe/param/OrderRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class OrderRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private OrderRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private OrderRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public OrderRetrieveParams build() {
-      return new OrderRetrieveParams(this.expand);
+      return new OrderRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * OrderRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link OrderRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/OrderReturnListParams.java b/src/main/java/com/stripe/param/OrderReturnListParams.java
index 50a6773b632..bf8a5b4bd18 100644
--- a/src/main/java/com/stripe/param/OrderReturnListParams.java
+++ b/src/main/java/com/stripe/param/OrderReturnListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class OrderReturnListParams extends ApiRequestParams {
   /** Date this return was created. */
@@ -25,6 +27,15 @@ public class OrderReturnListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -49,12 +60,14 @@ private OrderReturnListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String order,
       String startingAfter) {
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.order = order;
     this.startingAfter = startingAfter;
@@ -71,6 +84,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String order;
@@ -80,7 +95,13 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public OrderReturnListParams build() {
       return new OrderReturnListParams(
-          this.created, this.endingBefore, this.expand, this.limit, this.order, this.startingAfter);
+          this.created,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.order,
+          this.startingAfter);
     }
 
     /** Date this return was created. */
@@ -132,6 +153,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * OrderReturnListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link OrderReturnListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -160,6 +207,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -176,7 +232,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -188,6 +245,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -198,7 +257,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * OrderReturnListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link OrderReturnListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/OrderReturnOrderParams.java b/src/main/java/com/stripe/param/OrderReturnOrderParams.java
index 9d26add4a16..106b8035c84 100644
--- a/src/main/java/com/stripe/param/OrderReturnOrderParams.java
+++ b/src/main/java/com/stripe/param/OrderReturnOrderParams.java
@@ -6,7 +6,9 @@
 import com.stripe.net.ApiRequestParams;
 import com.stripe.param.common.EmptyParam;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class OrderReturnOrderParams extends ApiRequestParams {
@@ -14,12 +16,23 @@ public class OrderReturnOrderParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** List of items to return. */
   @SerializedName("items")
   Object items;
 
-  private OrderReturnOrderParams(List<String> expand, Object items) {
+  private OrderReturnOrderParams(
+      List<String> expand, Map<String, Object> extraParams, Object items) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.items = items;
   }
 
@@ -30,11 +43,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Object items;
 
     /** Finalize and obtain parameter instance from this builder. */
     public OrderReturnOrderParams build() {
-      return new OrderReturnOrderParams(this.expand, this.items);
+      return new OrderReturnOrderParams(this.expand, this.extraParams, this.items);
     }
 
     /**
@@ -63,6 +78,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * OrderReturnOrderParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link OrderReturnOrderParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** List of items to return. */
     public Builder setItems(EmptyParam items) {
       this.items = items;
@@ -85,6 +126,15 @@ public static class Item {
     @SerializedName("description")
     String description;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The ID of the SKU, tax, or shipping item being returned. */
     @SerializedName("parent")
     String parent;
@@ -97,9 +147,16 @@ public static class Item {
     @SerializedName("type")
     Type type;
 
-    private Item(Long amount, String description, String parent, Long quantity, Type type) {
+    private Item(
+        Long amount,
+        String description,
+        Map<String, Object> extraParams,
+        String parent,
+        Long quantity,
+        Type type) {
       this.amount = amount;
       this.description = description;
+      this.extraParams = extraParams;
       this.parent = parent;
       this.quantity = quantity;
       this.type = type;
@@ -114,6 +171,8 @@ public static class Builder {
 
       private String description;
 
+      private Map<String, Object> extraParams;
+
       private String parent;
 
       private Long quantity;
@@ -122,7 +181,8 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Item build() {
-        return new Item(this.amount, this.description, this.parent, this.quantity, this.type);
+        return new Item(
+            this.amount, this.description, this.extraParams, this.parent, this.quantity, this.type);
       }
 
       /** The amount (price) for this order item to return. */
@@ -137,6 +197,32 @@ public Builder setDescription(String description) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * OrderReturnOrderParams.Item#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link OrderReturnOrderParams.Item#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The ID of the SKU, tax, or shipping item being returned. */
       public Builder setParent(String parent) {
         this.parent = parent;
diff --git a/src/main/java/com/stripe/param/OrderReturnRetrieveParams.java b/src/main/java/com/stripe/param/OrderReturnRetrieveParams.java
index 210534c2456..f1ff3762efe 100644
--- a/src/main/java/com/stripe/param/OrderReturnRetrieveParams.java
+++ b/src/main/java/com/stripe/param/OrderReturnRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class OrderReturnRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private OrderReturnRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private OrderReturnRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public OrderReturnRetrieveParams build() {
-      return new OrderReturnRetrieveParams(this.expand);
+      return new OrderReturnRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * OrderReturnRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link OrderReturnRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/OrderUpdateParams.java b/src/main/java/com/stripe/param/OrderUpdateParams.java
index 84914e6bfc1..3cd8bd9d0ab 100644
--- a/src/main/java/com/stripe/param/OrderUpdateParams.java
+++ b/src/main/java/com/stripe/param/OrderUpdateParams.java
@@ -22,6 +22,15 @@ public class OrderUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to a product object. It can be useful for storing
    * additional information about the order in a structured format.
@@ -52,12 +61,14 @@ public class OrderUpdateParams extends ApiRequestParams {
   private OrderUpdateParams(
       String coupon,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String selectedShippingMethod,
       Shipping shipping,
       Status status) {
     this.coupon = coupon;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.selectedShippingMethod = selectedShippingMethod;
     this.shipping = shipping;
@@ -73,6 +84,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String selectedShippingMethod;
@@ -86,6 +99,7 @@ public OrderUpdateParams build() {
       return new OrderUpdateParams(
           this.coupon,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.selectedShippingMethod,
           this.shipping,
@@ -127,6 +141,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * OrderUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link OrderUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -185,12 +225,22 @@ public static class Shipping {
     @SerializedName("carrier")
     String carrier;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The tracking number provided by the carrier. */
     @SerializedName("tracking_number")
     String trackingNumber;
 
-    private Shipping(String carrier, String trackingNumber) {
+    private Shipping(String carrier, Map<String, Object> extraParams, String trackingNumber) {
       this.carrier = carrier;
+      this.extraParams = extraParams;
       this.trackingNumber = trackingNumber;
     }
 
@@ -201,11 +251,13 @@ public static Builder builder() {
     public static class Builder {
       private String carrier;
 
+      private Map<String, Object> extraParams;
+
       private String trackingNumber;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.carrier, this.trackingNumber);
+        return new Shipping(this.carrier, this.extraParams, this.trackingNumber);
       }
 
       /** The name of the carrier like `USPS`, `UPS`, or `FedEx`. */
@@ -214,6 +266,32 @@ public Builder setCarrier(String carrier) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * OrderUpdateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link OrderUpdateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The tracking number provided by the carrier. */
       public Builder setTrackingNumber(String trackingNumber) {
         this.trackingNumber = trackingNumber;
diff --git a/src/main/java/com/stripe/param/PaymentIntentCancelParams.java b/src/main/java/com/stripe/param/PaymentIntentCancelParams.java
index a3c8e25394c..444a09592ec 100644
--- a/src/main/java/com/stripe/param/PaymentIntentCancelParams.java
+++ b/src/main/java/com/stripe/param/PaymentIntentCancelParams.java
@@ -5,13 +5,15 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class PaymentIntentCancelParams extends ApiRequestParams {
   /**
    * Reason for canceling this PaymentIntent. If set, possible values are `duplicate`, `fraudulent`,
-   * `requested_by_customer`, or `failed_invoice`
+   * or `requested_by_customer`
    */
   @SerializedName("cancellation_reason")
   CancellationReason cancellationReason;
@@ -20,9 +22,20 @@ public class PaymentIntentCancelParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
-  private PaymentIntentCancelParams(CancellationReason cancellationReason, List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PaymentIntentCancelParams(
+      CancellationReason cancellationReason, List<String> expand, Map<String, Object> extraParams) {
     this.cancellationReason = cancellationReason;
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -34,14 +47,16 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentIntentCancelParams build() {
-      return new PaymentIntentCancelParams(this.cancellationReason, this.expand);
+      return new PaymentIntentCancelParams(this.cancellationReason, this.expand, this.extraParams);
     }
 
     /**
      * Reason for canceling this PaymentIntent. If set, possible values are `duplicate`,
-     * `fraudulent`, `requested_by_customer`, or `failed_invoice`
+     * `fraudulent`, or `requested_by_customer`
      */
     public Builder setCancellationReason(CancellationReason cancellationReason) {
       this.cancellationReason = cancellationReason;
@@ -73,6 +88,32 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentIntentCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentIntentCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 
   public enum CancellationReason implements ApiRequestParams.EnumParam {
diff --git a/src/main/java/com/stripe/param/PaymentIntentCaptureParams.java b/src/main/java/com/stripe/param/PaymentIntentCaptureParams.java
index 237d711ea4d..bb76395fc3e 100644
--- a/src/main/java/com/stripe/param/PaymentIntentCaptureParams.java
+++ b/src/main/java/com/stripe/param/PaymentIntentCaptureParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentIntentCaptureParams extends ApiRequestParams {
   /**
@@ -28,11 +30,24 @@ public class PaymentIntentCaptureParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   private PaymentIntentCaptureParams(
-      Long amountToCapture, Long applicationFeeAmount, List<String> expand) {
+      Long amountToCapture,
+      Long applicationFeeAmount,
+      List<String> expand,
+      Map<String, Object> extraParams) {
     this.amountToCapture = amountToCapture;
     this.applicationFeeAmount = applicationFeeAmount;
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -46,10 +61,12 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentIntentCaptureParams build() {
       return new PaymentIntentCaptureParams(
-          this.amountToCapture, this.applicationFeeAmount, this.expand);
+          this.amountToCapture, this.applicationFeeAmount, this.expand, this.extraParams);
     }
 
     /**
@@ -97,5 +114,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentIntentCaptureParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentIntentCaptureParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PaymentIntentConfirmParams.java b/src/main/java/com/stripe/param/PaymentIntentConfirmParams.java
index 4590151c2c5..161854d0a1e 100644
--- a/src/main/java/com/stripe/param/PaymentIntentConfirmParams.java
+++ b/src/main/java/com/stripe/param/PaymentIntentConfirmParams.java
@@ -6,13 +6,24 @@
 import com.stripe.net.ApiRequestParams;
 import com.stripe.param.common.EmptyParam;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentIntentConfirmParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** ID of the payment method to attach to this PaymentIntent. */
   @SerializedName("payment_method")
   String paymentMethod;
@@ -31,11 +42,13 @@ public class PaymentIntentConfirmParams extends ApiRequestParams {
   String returnUrl;
 
   /**
-   * Set to `true` to save the PaymentIntent's payment method (either `source` or `payment_method`)
-   * to the associated customer. If the payment method is already attached, this parameter does
-   * nothing. This parameter defaults to `false` and applies to the payment method passed in the
-   * same request or the current payment method attached to the PaymentIntent and must be specified
-   * again if a new payment method is added.
+   * Set to `true` to [save the PaymentIntent's payment
+   * method](https://stripe.com/docs/payments/payment-methods/saving) (either `source` or
+   * `payment_method`) to the associated customer. Defaults to `false`. If the payment method is
+   * already attached, this parameter does nothing. This parameter errors for payment methods that
+   * are not permitted to be attached to customers. The parameter applies to the payment method
+   * passed in the same request or the current payment method attached to the PaymentIntent and must
+   * be specified again if a new payment method is added.
    */
   @SerializedName("save_payment_method")
   Boolean savePaymentMethod;
@@ -50,6 +63,7 @@ public class PaymentIntentConfirmParams extends ApiRequestParams {
 
   private PaymentIntentConfirmParams(
       List<String> expand,
+      Map<String, Object> extraParams,
       String paymentMethod,
       String receiptEmail,
       String returnUrl,
@@ -57,6 +71,7 @@ private PaymentIntentConfirmParams(
       Object shipping,
       String source) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.paymentMethod = paymentMethod;
     this.receiptEmail = receiptEmail;
     this.returnUrl = returnUrl;
@@ -72,6 +87,8 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String paymentMethod;
 
     private String receiptEmail;
@@ -88,6 +105,7 @@ public static class Builder {
     public PaymentIntentConfirmParams build() {
       return new PaymentIntentConfirmParams(
           this.expand,
+          this.extraParams,
           this.paymentMethod,
           this.receiptEmail,
           this.returnUrl,
@@ -122,6 +140,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentIntentConfirmParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentIntentConfirmParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** ID of the payment method to attach to this PaymentIntent. */
     public Builder setPaymentMethod(String paymentMethod) {
       this.paymentMethod = paymentMethod;
@@ -146,9 +190,11 @@ public Builder setReturnUrl(String returnUrl) {
     }
 
     /**
-     * Set to `true` to save the PaymentIntent's payment method (either `source` or
-     * `payment_method`) to the associated customer. If the payment method is already attached, this
-     * parameter does nothing. This parameter defaults to `false` and applies to the payment method
+     * Set to `true` to [save the PaymentIntent's payment
+     * method](https://stripe.com/docs/payments/payment-methods/saving) (either `source` or
+     * `payment_method`) to the associated customer. Defaults to `false`. If the payment method is
+     * already attached, this parameter does nothing. This parameter errors for payment methods that
+     * are not permitted to be attached to customers. The parameter applies to the payment method
      * passed in the same request or the current payment method attached to the PaymentIntent and
      * must be specified again if a new payment method is added.
      */
@@ -185,6 +231,15 @@ public static class Shipping {
     @SerializedName("carrier")
     String carrier;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Recipient name. */
     @SerializedName("name")
     String name;
@@ -201,9 +256,15 @@ public static class Shipping {
     String trackingNumber;
 
     private Shipping(
-        Address address, String carrier, String name, String phone, String trackingNumber) {
+        Address address,
+        String carrier,
+        Map<String, Object> extraParams,
+        String name,
+        String phone,
+        String trackingNumber) {
       this.address = address;
       this.carrier = carrier;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
       this.trackingNumber = trackingNumber;
@@ -218,6 +279,8 @@ public static class Builder {
 
       private String carrier;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
@@ -226,7 +289,13 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.carrier, this.name, this.phone, this.trackingNumber);
+        return new Shipping(
+            this.address,
+            this.carrier,
+            this.extraParams,
+            this.name,
+            this.phone,
+            this.trackingNumber);
       }
 
       /** Shipping address. */
@@ -241,6 +310,32 @@ public Builder setCarrier(String carrier) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentIntentConfirmParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentIntentConfirmParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Recipient name. */
       public Builder setName(String name) {
         this.name = name;
@@ -270,6 +365,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -285,12 +389,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -306,6 +412,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -317,7 +425,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -330,6 +444,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentIntentConfirmParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentIntentConfirmParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
diff --git a/src/main/java/com/stripe/param/PaymentIntentCreateParams.java b/src/main/java/com/stripe/param/PaymentIntentCreateParams.java
index 7ae383d6b27..0400cda2f53 100644
--- a/src/main/java/com/stripe/param/PaymentIntentCreateParams.java
+++ b/src/main/java/com/stripe/param/PaymentIntentCreateParams.java
@@ -77,6 +77,15 @@ public class PaymentIntentCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -115,11 +124,13 @@ public class PaymentIntentCreateParams extends ApiRequestParams {
   String returnUrl;
 
   /**
-   * Set to `true` to save the PaymentIntent's payment method (either `source` or `payment_method`)
-   * to the associated customer. If the payment method is already attached, this parameter does
-   * nothing. This parameter defaults to `false` and applies to the payment method passed in the
-   * same request or the current payment method attached to the PaymentIntent and must be specified
-   * again if a new payment method is added.
+   * Set to `true` to [save the PaymentIntent's payment
+   * method](https://stripe.com/docs/payments/payment-methods/saving) (either `source` or
+   * `payment_method`) to the associated customer. Defaults to `false`. If the payment method is
+   * already attached, this parameter does nothing. This parameter errors for payment methods that
+   * are not permitted to be attached to customers. The parameter applies to the payment method
+   * passed in the same request or the current payment method attached to the PaymentIntent and must
+   * be specified again if a new payment method is added.
    */
   @SerializedName("save_payment_method")
   Boolean savePaymentMethod;
@@ -165,6 +176,7 @@ private PaymentIntentCreateParams(
       String customer,
       String description,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String onBehalfOf,
       String paymentMethod,
@@ -186,6 +198,7 @@ private PaymentIntentCreateParams(
     this.customer = customer;
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.onBehalfOf = onBehalfOf;
     this.paymentMethod = paymentMethod;
@@ -223,6 +236,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String onBehalfOf;
@@ -259,6 +274,7 @@ public PaymentIntentCreateParams build() {
           this.customer,
           this.description,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.onBehalfOf,
           this.paymentMethod,
@@ -377,6 +393,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentIntentCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentIntentCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -462,9 +504,11 @@ public Builder setReturnUrl(String returnUrl) {
     }
 
     /**
-     * Set to `true` to save the PaymentIntent's payment method (either `source` or
-     * `payment_method`) to the associated customer. If the payment method is already attached, this
-     * parameter does nothing. This parameter defaults to `false` and applies to the payment method
+     * Set to `true` to [save the PaymentIntent's payment
+     * method](https://stripe.com/docs/payments/payment-methods/saving) (either `source` or
+     * `payment_method`) to the associated customer. Defaults to `false`. If the payment method is
+     * already attached, this parameter does nothing. This parameter errors for payment methods that
+     * are not permitted to be attached to customers. The parameter applies to the payment method
      * passed in the same request or the current payment method attached to the PaymentIntent and
      * must be specified again if a new payment method is added.
      */
@@ -524,6 +568,15 @@ public static class Shipping {
     @SerializedName("carrier")
     String carrier;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Recipient name. */
     @SerializedName("name")
     String name;
@@ -540,9 +593,15 @@ public static class Shipping {
     String trackingNumber;
 
     private Shipping(
-        Address address, String carrier, String name, String phone, String trackingNumber) {
+        Address address,
+        String carrier,
+        Map<String, Object> extraParams,
+        String name,
+        String phone,
+        String trackingNumber) {
       this.address = address;
       this.carrier = carrier;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
       this.trackingNumber = trackingNumber;
@@ -557,6 +616,8 @@ public static class Builder {
 
       private String carrier;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
@@ -565,7 +626,13 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.carrier, this.name, this.phone, this.trackingNumber);
+        return new Shipping(
+            this.address,
+            this.carrier,
+            this.extraParams,
+            this.name,
+            this.phone,
+            this.trackingNumber);
       }
 
       /** Shipping address. */
@@ -580,6 +647,32 @@ public Builder setCarrier(String carrier) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentIntentCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentIntentCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Recipient name. */
       public Builder setName(String name) {
         this.name = name;
@@ -609,6 +702,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -624,12 +726,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -645,6 +749,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -656,7 +762,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -669,6 +781,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentIntentCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentIntentCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
@@ -701,8 +841,18 @@ public static class TransferData {
     @SerializedName("destination")
     String destination;
 
-    private TransferData(String destination) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private TransferData(String destination, Map<String, Object> extraParams) {
       this.destination = destination;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -712,9 +862,11 @@ public static Builder builder() {
     public static class Builder {
       private String destination;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public TransferData build() {
-        return new TransferData(this.destination);
+        return new TransferData(this.destination, this.extraParams);
       }
 
       /**
@@ -726,6 +878,32 @@ public Builder setDestination(String destination) {
         this.destination = destination;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentIntentCreateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentIntentCreateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 
diff --git a/src/main/java/com/stripe/param/PaymentIntentListParams.java b/src/main/java/com/stripe/param/PaymentIntentListParams.java
index 75e3aea01b9..3c8b4b1117d 100644
--- a/src/main/java/com/stripe/param/PaymentIntentListParams.java
+++ b/src/main/java/com/stripe/param/PaymentIntentListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentIntentListParams extends ApiRequestParams {
   /**
@@ -32,6 +34,15 @@ public class PaymentIntentListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -53,12 +64,14 @@ private PaymentIntentListParams(
       String customer,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter) {
     this.created = created;
     this.customer = customer;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -76,6 +89,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -87,6 +102,7 @@ public PaymentIntentListParams build() {
           this.customer,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter);
     }
@@ -152,6 +168,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentIntentListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentIntentListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -174,6 +216,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -190,7 +241,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -202,6 +254,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -212,7 +266,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentIntentListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentIntentListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/PaymentIntentRetrieveParams.java b/src/main/java/com/stripe/param/PaymentIntentRetrieveParams.java
index 29b1b466ca9..ccefb16da6a 100644
--- a/src/main/java/com/stripe/param/PaymentIntentRetrieveParams.java
+++ b/src/main/java/com/stripe/param/PaymentIntentRetrieveParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentIntentRetrieveParams extends ApiRequestParams {
   /**
@@ -19,9 +21,20 @@ public class PaymentIntentRetrieveParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
-  private PaymentIntentRetrieveParams(String clientSecret, List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PaymentIntentRetrieveParams(
+      String clientSecret, List<String> expand, Map<String, Object> extraParams) {
     this.clientSecret = clientSecret;
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -33,9 +46,11 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentIntentRetrieveParams build() {
-      return new PaymentIntentRetrieveParams(this.clientSecret, this.expand);
+      return new PaymentIntentRetrieveParams(this.clientSecret, this.expand, this.extraParams);
     }
 
     /**
@@ -72,5 +87,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentIntentRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentIntentRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PaymentIntentUpdateParams.java b/src/main/java/com/stripe/param/PaymentIntentUpdateParams.java
index ea076ebf458..eb01fb2aa46 100644
--- a/src/main/java/com/stripe/param/PaymentIntentUpdateParams.java
+++ b/src/main/java/com/stripe/param/PaymentIntentUpdateParams.java
@@ -42,6 +42,15 @@ public class PaymentIntentUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -62,11 +71,13 @@ public class PaymentIntentUpdateParams extends ApiRequestParams {
   String receiptEmail;
 
   /**
-   * Set to `true` to save the PaymentIntent's payment method (either `source` or `payment_method`)
-   * to the associated customer. If the payment method is already attached, this parameter does
-   * nothing. This parameter defaults to `false` and applies to the payment method passed in the
-   * same request or the current payment method attached to the PaymentIntent and must be specified
-   * again if a new payment method is added.
+   * Set to `true` to [save the PaymentIntent's payment
+   * method](https://stripe.com/docs/payments/payment-methods/saving) (either `source` or
+   * `payment_method`) to the associated customer. Defaults to `false`. If the payment method is
+   * already attached, this parameter does nothing. This parameter errors for payment methods that
+   * are not permitted to be attached to customers. The parameter applies to the payment method
+   * passed in the same request or the current payment method attached to the PaymentIntent and must
+   * be specified again if a new payment method is added.
    */
   @SerializedName("save_payment_method")
   Boolean savePaymentMethod;
@@ -101,6 +112,7 @@ private PaymentIntentUpdateParams(
       String customer,
       String description,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String paymentMethod,
       List<String> paymentMethodTypes,
@@ -116,6 +128,7 @@ private PaymentIntentUpdateParams(
     this.customer = customer;
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.paymentMethod = paymentMethod;
     this.paymentMethodTypes = paymentMethodTypes;
@@ -144,6 +157,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String paymentMethod;
@@ -171,6 +186,7 @@ public PaymentIntentUpdateParams build() {
           this.customer,
           this.description,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.paymentMethod,
           this.paymentMethodTypes,
@@ -255,6 +271,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentIntentUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentIntentUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -320,9 +362,11 @@ public Builder setReceiptEmail(String receiptEmail) {
     }
 
     /**
-     * Set to `true` to save the PaymentIntent's payment method (either `source` or
-     * `payment_method`) to the associated customer. If the payment method is already attached, this
-     * parameter does nothing. This parameter defaults to `false` and applies to the payment method
+     * Set to `true` to [save the PaymentIntent's payment
+     * method](https://stripe.com/docs/payments/payment-methods/saving) (either `source` or
+     * `payment_method`) to the associated customer. Defaults to `false`. If the payment method is
+     * already attached, this parameter does nothing. This parameter errors for payment methods that
+     * are not permitted to be attached to customers. The parameter applies to the payment method
      * passed in the same request or the current payment method attached to the PaymentIntent and
      * must be specified again if a new payment method is added.
      */
@@ -378,6 +422,15 @@ public static class Shipping {
     @SerializedName("carrier")
     String carrier;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Recipient name. */
     @SerializedName("name")
     String name;
@@ -394,9 +447,15 @@ public static class Shipping {
     String trackingNumber;
 
     private Shipping(
-        Address address, String carrier, String name, String phone, String trackingNumber) {
+        Address address,
+        String carrier,
+        Map<String, Object> extraParams,
+        String name,
+        String phone,
+        String trackingNumber) {
       this.address = address;
       this.carrier = carrier;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
       this.trackingNumber = trackingNumber;
@@ -411,6 +470,8 @@ public static class Builder {
 
       private String carrier;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
@@ -419,7 +480,13 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.carrier, this.name, this.phone, this.trackingNumber);
+        return new Shipping(
+            this.address,
+            this.carrier,
+            this.extraParams,
+            this.name,
+            this.phone,
+            this.trackingNumber);
       }
 
       /** Shipping address. */
@@ -434,6 +501,32 @@ public Builder setCarrier(String carrier) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentIntentUpdateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentIntentUpdateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Recipient name. */
       public Builder setName(String name) {
         this.name = name;
@@ -463,6 +556,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -478,12 +580,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -499,6 +603,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -510,7 +616,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -523,6 +635,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentIntentUpdateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentIntentUpdateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
diff --git a/src/main/java/com/stripe/param/PaymentMethodAttachParams.java b/src/main/java/com/stripe/param/PaymentMethodAttachParams.java
index 33933ba1de8..a57c6426108 100644
--- a/src/main/java/com/stripe/param/PaymentMethodAttachParams.java
+++ b/src/main/java/com/stripe/param/PaymentMethodAttachParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentMethodAttachParams extends ApiRequestParams {
   /** The ID of the customer to which to attach the PaymentMethod. */
@@ -16,9 +18,20 @@ public class PaymentMethodAttachParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
-  private PaymentMethodAttachParams(String customer, List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PaymentMethodAttachParams(
+      String customer, List<String> expand, Map<String, Object> extraParams) {
     this.customer = customer;
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -30,9 +43,11 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentMethodAttachParams build() {
-      return new PaymentMethodAttachParams(this.customer, this.expand);
+      return new PaymentMethodAttachParams(this.customer, this.expand, this.extraParams);
     }
 
     /** The ID of the customer to which to attach the PaymentMethod. */
@@ -66,5 +81,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentMethodAttachParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentMethodAttachParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PaymentMethodCreateParams.java b/src/main/java/com/stripe/param/PaymentMethodCreateParams.java
index 2a0957df018..8d9232185dd 100644
--- a/src/main/java/com/stripe/param/PaymentMethodCreateParams.java
+++ b/src/main/java/com/stripe/param/PaymentMethodCreateParams.java
@@ -37,6 +37,15 @@ public class PaymentMethodCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -63,6 +72,7 @@ private PaymentMethodCreateParams(
       Object card,
       String customer,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String paymentMethod,
       Type type) {
@@ -70,6 +80,7 @@ private PaymentMethodCreateParams(
     this.card = card;
     this.customer = customer;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.paymentMethod = paymentMethod;
     this.type = type;
@@ -88,6 +99,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String paymentMethod;
@@ -101,6 +114,7 @@ public PaymentMethodCreateParams build() {
           this.card,
           this.customer,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.paymentMethod,
           this.type);
@@ -173,6 +187,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentMethodCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentMethodCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -227,6 +267,15 @@ public static class BillingDetails {
     @SerializedName("email")
     String email;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Full name. */
     @SerializedName("name")
     String name;
@@ -235,9 +284,11 @@ public static class BillingDetails {
     @SerializedName("phone")
     String phone;
 
-    private BillingDetails(Address address, String email, String name, String phone) {
+    private BillingDetails(
+        Address address, String email, Map<String, Object> extraParams, String name, String phone) {
       this.address = address;
       this.email = email;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
     }
@@ -251,13 +302,16 @@ public static class Builder {
 
       private String email;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
 
       /** Finalize and obtain parameter instance from this builder. */
       public BillingDetails build() {
-        return new BillingDetails(this.address, this.email, this.name, this.phone);
+        return new BillingDetails(
+            this.address, this.email, this.extraParams, this.name, this.phone);
       }
 
       /** Billing address. */
@@ -272,6 +326,33 @@ public Builder setEmail(String email) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentMethodCreateParams.BillingDetails#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentMethodCreateParams.BillingDetails#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Full name. */
       public Builder setName(String name) {
         this.name = name;
@@ -292,6 +373,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -307,12 +397,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -328,6 +420,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -339,7 +433,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -352,6 +452,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentMethodCreateParams.BillingDetails.Address#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentMethodCreateParams.BillingDetails.Address#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
@@ -388,14 +516,25 @@ public static class CardDetails {
     @SerializedName("exp_year")
     Long expYear;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The card number, as a string without any separators. */
     @SerializedName("number")
     String number;
 
-    private CardDetails(String cvc, Long expMonth, Long expYear, String number) {
+    private CardDetails(
+        String cvc, Long expMonth, Long expYear, Map<String, Object> extraParams, String number) {
       this.cvc = cvc;
       this.expMonth = expMonth;
       this.expYear = expYear;
+      this.extraParams = extraParams;
       this.number = number;
     }
 
@@ -410,11 +549,14 @@ public static class Builder {
 
       private Long expYear;
 
+      private Map<String, Object> extraParams;
+
       private String number;
 
       /** Finalize and obtain parameter instance from this builder. */
       public CardDetails build() {
-        return new CardDetails(this.cvc, this.expMonth, this.expYear, this.number);
+        return new CardDetails(
+            this.cvc, this.expMonth, this.expYear, this.extraParams, this.number);
       }
 
       /** The card's CVC. It is highly recommended to always include this value. */
@@ -435,6 +577,32 @@ public Builder setExpYear(Long expYear) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentMethodCreateParams.CardDetails#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentMethodCreateParams.CardDetails#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The card number, as a string without any separators. */
       public Builder setNumber(String number) {
         this.number = number;
@@ -444,10 +612,20 @@ public Builder setNumber(String number) {
   }
 
   public static class Token {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("token")
     String token;
 
-    private Token(String token) {
+    private Token(Map<String, Object> extraParams, String token) {
+      this.extraParams = extraParams;
       this.token = token;
     }
 
@@ -456,11 +634,39 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String token;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Token build() {
-        return new Token(this.token);
+        return new Token(this.extraParams, this.token);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentMethodCreateParams.Token#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentMethodCreateParams.Token#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       public Builder setToken(String token) {
diff --git a/src/main/java/com/stripe/param/PaymentMethodDetachParams.java b/src/main/java/com/stripe/param/PaymentMethodDetachParams.java
index 1f97f8305a5..65b10534134 100644
--- a/src/main/java/com/stripe/param/PaymentMethodDetachParams.java
+++ b/src/main/java/com/stripe/param/PaymentMethodDetachParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentMethodDetachParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private PaymentMethodDetachParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PaymentMethodDetachParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentMethodDetachParams build() {
-      return new PaymentMethodDetachParams(this.expand);
+      return new PaymentMethodDetachParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentMethodDetachParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentMethodDetachParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PaymentMethodListParams.java b/src/main/java/com/stripe/param/PaymentMethodListParams.java
index d47264d8dea..33df3416efc 100644
--- a/src/main/java/com/stripe/param/PaymentMethodListParams.java
+++ b/src/main/java/com/stripe/param/PaymentMethodListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class PaymentMethodListParams extends ApiRequestParams {
@@ -26,6 +28,15 @@ public class PaymentMethodListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -50,12 +61,14 @@ private PaymentMethodListParams(
       String customer,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       Type type) {
     this.customer = customer;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.type = type;
@@ -72,6 +85,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -81,7 +96,13 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentMethodListParams build() {
       return new PaymentMethodListParams(
-          this.customer, this.endingBefore, this.expand, this.limit, this.startingAfter, this.type);
+          this.customer,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter,
+          this.type);
     }
 
     /** The ID of the customer whose PaymentMethods will be retrieved. */
@@ -127,6 +148,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentMethodListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentMethodListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/PaymentMethodRetrieveParams.java b/src/main/java/com/stripe/param/PaymentMethodRetrieveParams.java
index 1b25384d442..1f6da0041f4 100644
--- a/src/main/java/com/stripe/param/PaymentMethodRetrieveParams.java
+++ b/src/main/java/com/stripe/param/PaymentMethodRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentMethodRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private PaymentMethodRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PaymentMethodRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentMethodRetrieveParams build() {
-      return new PaymentMethodRetrieveParams(this.expand);
+      return new PaymentMethodRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentMethodRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentMethodRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PaymentMethodUpdateParams.java b/src/main/java/com/stripe/param/PaymentMethodUpdateParams.java
index d12156d17ed..4fd5d71b98d 100644
--- a/src/main/java/com/stripe/param/PaymentMethodUpdateParams.java
+++ b/src/main/java/com/stripe/param/PaymentMethodUpdateParams.java
@@ -24,6 +24,15 @@ public class PaymentMethodUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -32,10 +41,15 @@ public class PaymentMethodUpdateParams extends ApiRequestParams {
   Map<String, String> metadata;
 
   private PaymentMethodUpdateParams(
-      BillingDetails billingDetails, Card card, List<String> expand, Map<String, String> metadata) {
+      BillingDetails billingDetails,
+      Card card,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata) {
     this.billingDetails = billingDetails;
     this.card = card;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -50,12 +64,14 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentMethodUpdateParams build() {
       return new PaymentMethodUpdateParams(
-          this.billingDetails, this.card, this.expand, this.metadata);
+          this.billingDetails, this.card, this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -98,6 +114,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentMethodUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentMethodUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -134,6 +176,15 @@ public static class BillingDetails {
     @SerializedName("email")
     String email;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Full name. */
     @SerializedName("name")
     String name;
@@ -142,9 +193,11 @@ public static class BillingDetails {
     @SerializedName("phone")
     String phone;
 
-    private BillingDetails(Address address, String email, String name, String phone) {
+    private BillingDetails(
+        Address address, String email, Map<String, Object> extraParams, String name, String phone) {
       this.address = address;
       this.email = email;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
     }
@@ -158,13 +211,16 @@ public static class Builder {
 
       private String email;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
 
       /** Finalize and obtain parameter instance from this builder. */
       public BillingDetails build() {
-        return new BillingDetails(this.address, this.email, this.name, this.phone);
+        return new BillingDetails(
+            this.address, this.email, this.extraParams, this.name, this.phone);
       }
 
       /** Billing address. */
@@ -179,6 +235,33 @@ public Builder setEmail(String email) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentMethodUpdateParams.BillingDetails#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentMethodUpdateParams.BillingDetails#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Full name. */
       public Builder setName(String name) {
         this.name = name;
@@ -199,6 +282,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -214,12 +306,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -235,6 +329,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -246,7 +342,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -259,6 +361,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentMethodUpdateParams.BillingDetails.Address#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PaymentMethodUpdateParams.BillingDetails.Address#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
@@ -291,9 +421,19 @@ public static class Card {
     @SerializedName("exp_year")
     Long expYear;
 
-    private Card(Long expMonth, Long expYear) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private Card(Long expMonth, Long expYear, Map<String, Object> extraParams) {
       this.expMonth = expMonth;
       this.expYear = expYear;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -305,9 +445,11 @@ public static class Builder {
 
       private Long expYear;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public Card build() {
-        return new Card(this.expMonth, this.expYear);
+        return new Card(this.expMonth, this.expYear, this.extraParams);
       }
 
       /** Two-digit number representing the card's expiration month. */
@@ -321,6 +463,32 @@ public Builder setExpYear(Long expYear) {
         this.expYear = expYear;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PaymentMethodUpdateParams.Card#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PaymentMethodUpdateParams.Card#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 }
diff --git a/src/main/java/com/stripe/param/PaymentSourceCollectionCreateParams.java b/src/main/java/com/stripe/param/PaymentSourceCollectionCreateParams.java
index d8b7597e881..5806946b2e5 100644
--- a/src/main/java/com/stripe/param/PaymentSourceCollectionCreateParams.java
+++ b/src/main/java/com/stripe/param/PaymentSourceCollectionCreateParams.java
@@ -14,6 +14,15 @@ public class PaymentSourceCollectionCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to a card object. It can be useful for storing
    * additional information about the card in a structured format.
@@ -26,8 +35,12 @@ public class PaymentSourceCollectionCreateParams extends ApiRequestParams {
   String source;
 
   private PaymentSourceCollectionCreateParams(
-      List<String> expand, Map<String, String> metadata, String source) {
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata,
+      String source) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.source = source;
   }
@@ -39,13 +52,16 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String source;
 
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentSourceCollectionCreateParams build() {
-      return new PaymentSourceCollectionCreateParams(this.expand, this.metadata, this.source);
+      return new PaymentSourceCollectionCreateParams(
+          this.expand, this.extraParams, this.metadata, this.source);
     }
 
     /**
@@ -74,6 +90,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentSourceCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentSourceCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/PaymentSourceCollectionListParams.java b/src/main/java/com/stripe/param/PaymentSourceCollectionListParams.java
index 80df90849b7..196d7f54cdc 100644
--- a/src/main/java/com/stripe/param/PaymentSourceCollectionListParams.java
+++ b/src/main/java/com/stripe/param/PaymentSourceCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentSourceCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class PaymentSourceCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -42,9 +53,15 @@ public class PaymentSourceCollectionListParams extends ApiRequestParams {
   String startingAfter;
 
   private PaymentSourceCollectionListParams(
-      String endingBefore, List<String> expand, Long limit, String object, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String object,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.object = object;
     this.startingAfter = startingAfter;
@@ -59,6 +76,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String object;
@@ -68,7 +87,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentSourceCollectionListParams build() {
       return new PaymentSourceCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.object, this.startingAfter);
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.object,
+          this.startingAfter);
     }
 
     /**
@@ -108,6 +132,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentSourceCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentSourceCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/PaymentSourceCollectionRetrieveParams.java b/src/main/java/com/stripe/param/PaymentSourceCollectionRetrieveParams.java
index a0d7df59928..dfe29f8a421 100644
--- a/src/main/java/com/stripe/param/PaymentSourceCollectionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/PaymentSourceCollectionRetrieveParams.java
@@ -5,15 +5,28 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PaymentSourceCollectionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private PaymentSourceCollectionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PaymentSourceCollectionRetrieveParams(
+      List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +36,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PaymentSourceCollectionRetrieveParams build() {
-      return new PaymentSourceCollectionRetrieveParams(this.expand);
+      return new PaymentSourceCollectionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +68,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PaymentSourceCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PaymentSourceCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PayoutCancelParams.java b/src/main/java/com/stripe/param/PayoutCancelParams.java
index 3321ce35508..1ac46d5b753 100644
--- a/src/main/java/com/stripe/param/PayoutCancelParams.java
+++ b/src/main/java/com/stripe/param/PayoutCancelParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PayoutCancelParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private PayoutCancelParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PayoutCancelParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PayoutCancelParams build() {
-      return new PayoutCancelParams(this.expand);
+      return new PayoutCancelParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PayoutCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PayoutCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PayoutCreateParams.java b/src/main/java/com/stripe/param/PayoutCreateParams.java
index 26a9f51efc9..7d2d9d950c8 100644
--- a/src/main/java/com/stripe/param/PayoutCreateParams.java
+++ b/src/main/java/com/stripe/param/PayoutCreateParams.java
@@ -37,6 +37,15 @@ public class PayoutCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to a payout object. It can be useful for storing
    * additional information about the payout in a structured format.
@@ -74,6 +83,7 @@ private PayoutCreateParams(
       String description,
       String destination,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       Method method,
       SourceType sourceType,
@@ -83,6 +93,7 @@ private PayoutCreateParams(
     this.description = description;
     this.destination = destination;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.method = method;
     this.sourceType = sourceType;
@@ -104,6 +115,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private Method method;
@@ -120,6 +133,7 @@ public PayoutCreateParams build() {
           this.description,
           this.destination,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.method,
           this.sourceType,
@@ -182,6 +196,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PayoutCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PayoutCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/PayoutListParams.java b/src/main/java/com/stripe/param/PayoutListParams.java
index a383c3ba314..da6bd61dc90 100644
--- a/src/main/java/com/stripe/param/PayoutListParams.java
+++ b/src/main/java/com/stripe/param/PayoutListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PayoutListParams extends ApiRequestParams {
   @SerializedName("arrival_date")
@@ -31,6 +33,15 @@ public class PayoutListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -57,6 +68,7 @@ private PayoutListParams(
       String destination,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       String status) {
@@ -65,6 +77,7 @@ private PayoutListParams(
     this.destination = destination;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.status = status;
@@ -85,6 +98,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -99,6 +114,7 @@ public PayoutListParams build() {
           this.destination,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter,
           this.status);
@@ -167,6 +183,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PayoutListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PayoutListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -197,6 +239,15 @@ public Builder setStatus(String status) {
   }
 
   public static class ArrivalDate {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -213,7 +264,8 @@ public static class ArrivalDate {
     @SerializedName("lte")
     Long lte;
 
-    private ArrivalDate(Long gt, Long gte, Long lt, Long lte) {
+    private ArrivalDate(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -225,6 +277,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -235,7 +289,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public ArrivalDate build() {
-        return new ArrivalDate(this.gt, this.gte, this.lt, this.lte);
+        return new ArrivalDate(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PayoutListParams.ArrivalDate#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PayoutListParams.ArrivalDate#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -265,6 +345,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -281,7 +370,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -293,6 +383,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -303,7 +395,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PayoutListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PayoutListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/PayoutRetrieveParams.java b/src/main/java/com/stripe/param/PayoutRetrieveParams.java
index e3314846176..9202a5a2c27 100644
--- a/src/main/java/com/stripe/param/PayoutRetrieveParams.java
+++ b/src/main/java/com/stripe/param/PayoutRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PayoutRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private PayoutRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PayoutRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PayoutRetrieveParams build() {
-      return new PayoutRetrieveParams(this.expand);
+      return new PayoutRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PayoutRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PayoutRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PayoutUpdateParams.java b/src/main/java/com/stripe/param/PayoutUpdateParams.java
index e7fb51c4f70..599d943bbc4 100644
--- a/src/main/java/com/stripe/param/PayoutUpdateParams.java
+++ b/src/main/java/com/stripe/param/PayoutUpdateParams.java
@@ -14,6 +14,15 @@ public class PayoutUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to a payout object. It can be useful for storing
    * additional information about the payout in a structured format.
@@ -21,8 +30,10 @@ public class PayoutUpdateParams extends ApiRequestParams {
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private PayoutUpdateParams(List<String> expand, Map<String, String> metadata) {
+  private PayoutUpdateParams(
+      List<String> expand, Map<String, Object> extraParams, Map<String, String> metadata) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -33,11 +44,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public PayoutUpdateParams build() {
-      return new PayoutUpdateParams(this.expand, this.metadata);
+      return new PayoutUpdateParams(this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -66,6 +79,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PayoutUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PayoutUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/PersonCollectionCreateParams.java b/src/main/java/com/stripe/param/PersonCollectionCreateParams.java
index 90176d1cba1..c25f3678c0b 100644
--- a/src/main/java/com/stripe/param/PersonCollectionCreateParams.java
+++ b/src/main/java/com/stripe/param/PersonCollectionCreateParams.java
@@ -36,6 +36,15 @@ public class PersonCollectionCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The person's first name. */
   @SerializedName("first_name")
   String firstName;
@@ -115,6 +124,7 @@ private PersonCollectionCreateParams(
       Dob dob,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       String firstName,
       String firstNameKana,
       String firstNameKanji,
@@ -136,6 +146,7 @@ private PersonCollectionCreateParams(
     this.dob = dob;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.firstName = firstName;
     this.firstNameKana = firstNameKana;
     this.firstNameKanji = firstNameKanji;
@@ -170,6 +181,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String firstName;
 
     private String firstNameKana;
@@ -209,6 +222,7 @@ public PersonCollectionCreateParams build() {
           this.dob,
           this.email,
           this.expand,
+          this.extraParams,
           this.firstName,
           this.firstNameKana,
           this.firstNameKanji,
@@ -282,6 +296,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PersonCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PersonCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The person's first name. */
     public Builder setFirstName(String firstName) {
       this.firstName = firstName;
@@ -413,6 +453,15 @@ public static class Address {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Address line 1 (e.g., street, PO Box, or company name). */
     @SerializedName("line1")
     String line1;
@@ -430,9 +479,16 @@ public static class Address {
     String state;
 
     private Address(
-        String city, String country, String line1, String line2, String postalCode, String state) {
+        String city,
+        String country,
+        Map<String, Object> extraParams,
+        String line1,
+        String line2,
+        String postalCode,
+        String state) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -448,6 +504,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -459,7 +517,13 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Address build() {
         return new Address(
-            this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+            this.city,
+            this.country,
+            this.extraParams,
+            this.line1,
+            this.line2,
+            this.postalCode,
+            this.state);
       }
 
       /** City, district, suburb, town, or village. */
@@ -477,6 +541,32 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonCollectionCreateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonCollectionCreateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Address line 1 (e.g., street, PO Box, or company name). */
       public Builder setLine1(String line1) {
         this.line1 = line1;
@@ -515,6 +605,15 @@ public static class AddressKana {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Block or building number. */
     @SerializedName("line1")
     String line1;
@@ -538,6 +637,7 @@ public static class AddressKana {
     private AddressKana(
         String city,
         String country,
+        Map<String, Object> extraParams,
         String line1,
         String line2,
         String postalCode,
@@ -545,6 +645,7 @@ private AddressKana(
         String town) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -561,6 +662,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -576,6 +679,7 @@ public AddressKana build() {
         return new AddressKana(
             this.city,
             this.country,
+            this.extraParams,
             this.line1,
             this.line2,
             this.postalCode,
@@ -598,6 +702,33 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonCollectionCreateParams.AddressKana#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonCollectionCreateParams.AddressKana#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Block or building number. */
       public Builder setLine1(String line1) {
         this.line1 = line1;
@@ -642,6 +773,15 @@ public static class AddressKanji {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Block or building number. */
     @SerializedName("line1")
     String line1;
@@ -665,6 +805,7 @@ public static class AddressKanji {
     private AddressKanji(
         String city,
         String country,
+        Map<String, Object> extraParams,
         String line1,
         String line2,
         String postalCode,
@@ -672,6 +813,7 @@ private AddressKanji(
         String town) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -688,6 +830,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -703,6 +847,7 @@ public AddressKanji build() {
         return new AddressKanji(
             this.city,
             this.country,
+            this.extraParams,
             this.line1,
             this.line2,
             this.postalCode,
@@ -725,6 +870,33 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonCollectionCreateParams.AddressKanji#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonCollectionCreateParams.AddressKanji#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Block or building number. */
       public Builder setLine1(String line1) {
         this.line1 = line1;
@@ -762,6 +934,15 @@ public static class Dob {
     @SerializedName("day")
     Long day;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The month of birth, between 1 and 12. */
     @SerializedName("month")
     Long month;
@@ -770,8 +951,9 @@ public static class Dob {
     @SerializedName("year")
     Long year;
 
-    private Dob(Long day, Long month, Long year) {
+    private Dob(Long day, Map<String, Object> extraParams, Long month, Long year) {
       this.day = day;
+      this.extraParams = extraParams;
       this.month = month;
       this.year = year;
     }
@@ -783,13 +965,15 @@ public static Builder builder() {
     public static class Builder {
       private Long day;
 
+      private Map<String, Object> extraParams;
+
       private Long month;
 
       private Long year;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Dob build() {
-        return new Dob(this.day, this.month, this.year);
+        return new Dob(this.day, this.extraParams, this.month, this.year);
       }
 
       /** The day of birth, between 1 and 31. */
@@ -798,6 +982,32 @@ public Builder setDay(Long day) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonCollectionCreateParams.Dob#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonCollectionCreateParams.Dob#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The month of birth, between 1 and 12. */
       public Builder setMonth(Long month) {
         this.month = month;
@@ -828,6 +1038,15 @@ public static class Relationship {
     @SerializedName("director")
     Boolean director;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Whether the person is an owner of the account’s legal entity. */
     @SerializedName("owner")
     Boolean owner;
@@ -843,11 +1062,13 @@ public static class Relationship {
     private Relationship(
         Boolean accountOpener,
         Boolean director,
+        Map<String, Object> extraParams,
         Boolean owner,
         Object percentOwnership,
         String title) {
       this.accountOpener = accountOpener;
       this.director = director;
+      this.extraParams = extraParams;
       this.owner = owner;
       this.percentOwnership = percentOwnership;
       this.title = title;
@@ -862,6 +1083,8 @@ public static class Builder {
 
       private Boolean director;
 
+      private Map<String, Object> extraParams;
+
       private Boolean owner;
 
       private Object percentOwnership;
@@ -871,7 +1094,12 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Relationship build() {
         return new Relationship(
-            this.accountOpener, this.director, this.owner, this.percentOwnership, this.title);
+            this.accountOpener,
+            this.director,
+            this.extraParams,
+            this.owner,
+            this.percentOwnership,
+            this.title);
       }
 
       /**
@@ -893,6 +1121,33 @@ public Builder setDirector(Boolean director) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonCollectionCreateParams.Relationship#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonCollectionCreateParams.Relationship#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Whether the person is an owner of the account’s legal entity. */
       public Builder setOwner(Boolean owner) {
         this.owner = owner;
@@ -924,8 +1179,18 @@ public static class Verification {
     @SerializedName("document")
     Document document;
 
-    private Verification(Document document) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private Verification(Document document, Map<String, Object> extraParams) {
       this.document = document;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -935,9 +1200,11 @@ public static Builder builder() {
     public static class Builder {
       private Document document;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public Verification build() {
-        return new Verification(this.document);
+        return new Verification(this.document, this.extraParams);
       }
 
       /** An identifying document, either a passport or local ID card. */
@@ -945,6 +1212,33 @@ public Builder setDocument(Document document) {
         this.document = document;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonCollectionCreateParams.Verification#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonCollectionCreateParams.Verification#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
 
     public static class Document {
@@ -955,6 +1249,15 @@ public static class Document {
       @SerializedName("back")
       String back;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The front of an ID returned by a [file upload](#create_file) with a `purpose` value of
        * `identity_document`.
@@ -962,8 +1265,9 @@ public static class Document {
       @SerializedName("front")
       String front;
 
-      private Document(String back, String front) {
+      private Document(String back, Map<String, Object> extraParams, String front) {
         this.back = back;
+        this.extraParams = extraParams;
         this.front = front;
       }
 
@@ -974,11 +1278,13 @@ public static Builder builder() {
       public static class Builder {
         private String back;
 
+        private Map<String, Object> extraParams;
+
         private String front;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Document build() {
-          return new Document(this.back, this.front);
+          return new Document(this.back, this.extraParams, this.front);
         }
 
         /**
@@ -990,6 +1296,34 @@ public Builder setBack(String back) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PersonCollectionCreateParams.Verification.Document#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PersonCollectionCreateParams.Verification.Document#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * The front of an ID returned by a [file upload](#create_file) with a `purpose` value of
          * `identity_document`.
diff --git a/src/main/java/com/stripe/param/PersonCollectionListParams.java b/src/main/java/com/stripe/param/PersonCollectionListParams.java
index 0ad15e829e0..644b57648ee 100644
--- a/src/main/java/com/stripe/param/PersonCollectionListParams.java
+++ b/src/main/java/com/stripe/param/PersonCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PersonCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class PersonCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -47,11 +58,13 @@ public class PersonCollectionListParams extends ApiRequestParams {
   private PersonCollectionListParams(
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       Relationship relationship,
       String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.relationship = relationship;
     this.startingAfter = startingAfter;
@@ -66,6 +79,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private Relationship relationship;
@@ -75,7 +90,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public PersonCollectionListParams build() {
       return new PersonCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.relationship, this.startingAfter);
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.relationship,
+          this.startingAfter);
     }
 
     /**
@@ -115,6 +135,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PersonCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PersonCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -160,6 +206,15 @@ public static class Relationship {
     @SerializedName("director")
     Boolean director;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * A filter on the list of people returned based on whether these people are owners of the
      * account's company.
@@ -167,9 +222,11 @@ public static class Relationship {
     @SerializedName("owner")
     Boolean owner;
 
-    private Relationship(Boolean accountOpener, Boolean director, Boolean owner) {
+    private Relationship(
+        Boolean accountOpener, Boolean director, Map<String, Object> extraParams, Boolean owner) {
       this.accountOpener = accountOpener;
       this.director = director;
+      this.extraParams = extraParams;
       this.owner = owner;
     }
 
@@ -182,11 +239,13 @@ public static class Builder {
 
       private Boolean director;
 
+      private Map<String, Object> extraParams;
+
       private Boolean owner;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Relationship build() {
-        return new Relationship(this.accountOpener, this.director, this.owner);
+        return new Relationship(this.accountOpener, this.director, this.extraParams, this.owner);
       }
 
       /**
@@ -207,6 +266,33 @@ public Builder setDirector(Boolean director) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonCollectionListParams.Relationship#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonCollectionListParams.Relationship#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * A filter on the list of people returned based on whether these people are owners of the
        * account's company.
diff --git a/src/main/java/com/stripe/param/PersonCollectionRetrieveParams.java b/src/main/java/com/stripe/param/PersonCollectionRetrieveParams.java
index 79748b19094..ccb82b0f9ce 100644
--- a/src/main/java/com/stripe/param/PersonCollectionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/PersonCollectionRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PersonCollectionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private PersonCollectionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PersonCollectionRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PersonCollectionRetrieveParams build() {
-      return new PersonCollectionRetrieveParams(this.expand);
+      return new PersonCollectionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PersonCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PersonCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PersonUpdateParams.java b/src/main/java/com/stripe/param/PersonUpdateParams.java
index 8ee9e65bcb7..2efbe63df4e 100644
--- a/src/main/java/com/stripe/param/PersonUpdateParams.java
+++ b/src/main/java/com/stripe/param/PersonUpdateParams.java
@@ -36,6 +36,15 @@ public class PersonUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The person's first name. */
   @SerializedName("first_name")
   String firstName;
@@ -115,6 +124,7 @@ private PersonUpdateParams(
       Dob dob,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       String firstName,
       String firstNameKana,
       String firstNameKanji,
@@ -136,6 +146,7 @@ private PersonUpdateParams(
     this.dob = dob;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.firstName = firstName;
     this.firstNameKana = firstNameKana;
     this.firstNameKanji = firstNameKanji;
@@ -170,6 +181,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String firstName;
 
     private String firstNameKana;
@@ -209,6 +222,7 @@ public PersonUpdateParams build() {
           this.dob,
           this.email,
           this.expand,
+          this.extraParams,
           this.firstName,
           this.firstNameKana,
           this.firstNameKanji,
@@ -282,6 +296,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PersonUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PersonUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The person's first name. */
     public Builder setFirstName(String firstName) {
       this.firstName = firstName;
@@ -413,6 +453,15 @@ public static class Address {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Address line 1 (e.g., street, PO Box, or company name). */
     @SerializedName("line1")
     String line1;
@@ -430,9 +479,16 @@ public static class Address {
     String state;
 
     private Address(
-        String city, String country, String line1, String line2, String postalCode, String state) {
+        String city,
+        String country,
+        Map<String, Object> extraParams,
+        String line1,
+        String line2,
+        String postalCode,
+        String state) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -448,6 +504,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -459,7 +517,13 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Address build() {
         return new Address(
-            this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+            this.city,
+            this.country,
+            this.extraParams,
+            this.line1,
+            this.line2,
+            this.postalCode,
+            this.state);
       }
 
       /** City, district, suburb, town, or village. */
@@ -477,6 +541,32 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonUpdateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonUpdateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Address line 1 (e.g., street, PO Box, or company name). */
       public Builder setLine1(String line1) {
         this.line1 = line1;
@@ -515,6 +605,15 @@ public static class AddressKana {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Block or building number. */
     @SerializedName("line1")
     String line1;
@@ -538,6 +637,7 @@ public static class AddressKana {
     private AddressKana(
         String city,
         String country,
+        Map<String, Object> extraParams,
         String line1,
         String line2,
         String postalCode,
@@ -545,6 +645,7 @@ private AddressKana(
         String town) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -561,6 +662,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -576,6 +679,7 @@ public AddressKana build() {
         return new AddressKana(
             this.city,
             this.country,
+            this.extraParams,
             this.line1,
             this.line2,
             this.postalCode,
@@ -598,6 +702,32 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonUpdateParams.AddressKana#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonUpdateParams.AddressKana#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Block or building number. */
       public Builder setLine1(String line1) {
         this.line1 = line1;
@@ -642,6 +772,15 @@ public static class AddressKanji {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Block or building number. */
     @SerializedName("line1")
     String line1;
@@ -665,6 +804,7 @@ public static class AddressKanji {
     private AddressKanji(
         String city,
         String country,
+        Map<String, Object> extraParams,
         String line1,
         String line2,
         String postalCode,
@@ -672,6 +812,7 @@ private AddressKanji(
         String town) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -688,6 +829,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -703,6 +846,7 @@ public AddressKanji build() {
         return new AddressKanji(
             this.city,
             this.country,
+            this.extraParams,
             this.line1,
             this.line2,
             this.postalCode,
@@ -725,6 +869,32 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonUpdateParams.AddressKanji#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonUpdateParams.AddressKanji#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Block or building number. */
       public Builder setLine1(String line1) {
         this.line1 = line1;
@@ -762,6 +932,15 @@ public static class Dob {
     @SerializedName("day")
     Long day;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The month of birth, between 1 and 12. */
     @SerializedName("month")
     Long month;
@@ -770,8 +949,9 @@ public static class Dob {
     @SerializedName("year")
     Long year;
 
-    private Dob(Long day, Long month, Long year) {
+    private Dob(Long day, Map<String, Object> extraParams, Long month, Long year) {
       this.day = day;
+      this.extraParams = extraParams;
       this.month = month;
       this.year = year;
     }
@@ -783,13 +963,15 @@ public static Builder builder() {
     public static class Builder {
       private Long day;
 
+      private Map<String, Object> extraParams;
+
       private Long month;
 
       private Long year;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Dob build() {
-        return new Dob(this.day, this.month, this.year);
+        return new Dob(this.day, this.extraParams, this.month, this.year);
       }
 
       /** The day of birth, between 1 and 31. */
@@ -798,6 +980,32 @@ public Builder setDay(Long day) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonUpdateParams.Dob#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonUpdateParams.Dob#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** The month of birth, between 1 and 12. */
       public Builder setMonth(Long month) {
         this.month = month;
@@ -828,6 +1036,15 @@ public static class Relationship {
     @SerializedName("director")
     Boolean director;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Whether the person is an owner of the account’s legal entity. */
     @SerializedName("owner")
     Boolean owner;
@@ -843,11 +1060,13 @@ public static class Relationship {
     private Relationship(
         Boolean accountOpener,
         Boolean director,
+        Map<String, Object> extraParams,
         Boolean owner,
         Object percentOwnership,
         String title) {
       this.accountOpener = accountOpener;
       this.director = director;
+      this.extraParams = extraParams;
       this.owner = owner;
       this.percentOwnership = percentOwnership;
       this.title = title;
@@ -862,6 +1081,8 @@ public static class Builder {
 
       private Boolean director;
 
+      private Map<String, Object> extraParams;
+
       private Boolean owner;
 
       private Object percentOwnership;
@@ -871,7 +1092,12 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Relationship build() {
         return new Relationship(
-            this.accountOpener, this.director, this.owner, this.percentOwnership, this.title);
+            this.accountOpener,
+            this.director,
+            this.extraParams,
+            this.owner,
+            this.percentOwnership,
+            this.title);
       }
 
       /**
@@ -893,6 +1119,32 @@ public Builder setDirector(Boolean director) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonUpdateParams.Relationship#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonUpdateParams.Relationship#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Whether the person is an owner of the account’s legal entity. */
       public Builder setOwner(Boolean owner) {
         this.owner = owner;
@@ -924,8 +1176,18 @@ public static class Verification {
     @SerializedName("document")
     Document document;
 
-    private Verification(Document document) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private Verification(Document document, Map<String, Object> extraParams) {
       this.document = document;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -935,9 +1197,11 @@ public static Builder builder() {
     public static class Builder {
       private Document document;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public Verification build() {
-        return new Verification(this.document);
+        return new Verification(this.document, this.extraParams);
       }
 
       /** An identifying document, either a passport or local ID card. */
@@ -945,6 +1209,32 @@ public Builder setDocument(Document document) {
         this.document = document;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PersonUpdateParams.Verification#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PersonUpdateParams.Verification#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
 
     public static class Document {
@@ -955,6 +1245,15 @@ public static class Document {
       @SerializedName("back")
       String back;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The front of an ID returned by a [file upload](#create_file) with a `purpose` value of
        * `identity_document`.
@@ -962,8 +1261,9 @@ public static class Document {
       @SerializedName("front")
       String front;
 
-      private Document(String back, String front) {
+      private Document(String back, Map<String, Object> extraParams, String front) {
         this.back = back;
+        this.extraParams = extraParams;
         this.front = front;
       }
 
@@ -974,11 +1274,13 @@ public static Builder builder() {
       public static class Builder {
         private String back;
 
+        private Map<String, Object> extraParams;
+
         private String front;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Document build() {
-          return new Document(this.back, this.front);
+          return new Document(this.back, this.extraParams, this.front);
         }
 
         /**
@@ -990,6 +1292,34 @@ public Builder setBack(String back) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PersonUpdateParams.Verification.Document#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link PersonUpdateParams.Verification.Document#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * The front of an ID returned by a [file upload](#create_file) with a `purpose` value of
          * `identity_document`.
diff --git a/src/main/java/com/stripe/param/PlanCreateParams.java b/src/main/java/com/stripe/param/PlanCreateParams.java
index fa135ce3e10..bc98195ef47 100644
--- a/src/main/java/com/stripe/param/PlanCreateParams.java
+++ b/src/main/java/com/stripe/param/PlanCreateParams.java
@@ -53,6 +53,15 @@ public class PlanCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * An identifier randomly generated by Stripe. Used to identify this plan when subscribing a
    * customer. You can optionally override this ID, but the ID must be unique across all plans in
@@ -132,6 +141,7 @@ private PlanCreateParams(
       BillingScheme billingScheme,
       String currency,
       List<String> expand,
+      Map<String, Object> extraParams,
       String id,
       Interval interval,
       Long intervalCount,
@@ -149,6 +159,7 @@ private PlanCreateParams(
     this.billingScheme = billingScheme;
     this.currency = currency;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.id = id;
     this.interval = interval;
     this.intervalCount = intervalCount;
@@ -179,6 +190,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String id;
 
     private Interval interval;
@@ -210,6 +223,7 @@ public PlanCreateParams build() {
           this.billingScheme,
           this.currency,
           this.expand,
+          this.extraParams,
           this.id,
           this.interval,
           this.intervalCount,
@@ -297,6 +311,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PlanCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PlanCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * An identifier randomly generated by Stripe. Used to identify this plan when subscribing a
      * customer. You can optionally override this ID, but the ID must be unique across all plans in
@@ -436,6 +476,15 @@ public static class Product {
     @SerializedName("active")
     Boolean active;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The identifier for the product. Must be unique. If not provided, an identifier will be
      * randomly generated.
@@ -459,8 +508,14 @@ public static class Product {
     @SerializedName("unit_label")
     String unitLabel;
 
-    private Product(Boolean active, String id, Map<String, String> metadata, String unitLabel) {
+    private Product(
+        Boolean active,
+        Map<String, Object> extraParams,
+        String id,
+        Map<String, String> metadata,
+        String unitLabel) {
       this.active = active;
+      this.extraParams = extraParams;
       this.id = id;
       this.metadata = metadata;
       this.unitLabel = unitLabel;
@@ -473,6 +528,8 @@ public static Builder builder() {
     public static class Builder {
       private Boolean active;
 
+      private Map<String, Object> extraParams;
+
       private String id;
 
       private Map<String, String> metadata;
@@ -481,7 +538,7 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Product build() {
-        return new Product(this.active, this.id, this.metadata, this.unitLabel);
+        return new Product(this.active, this.extraParams, this.id, this.metadata, this.unitLabel);
       }
 
       /** Whether the product is currently available for purchase. Defaults to `true`. */
@@ -490,6 +547,32 @@ public Builder setActive(Boolean active) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PlanCreateParams.Product#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PlanCreateParams.Product#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * The identifier for the product. Must be unique. If not provided, an identifier will be
        * randomly generated.
@@ -537,6 +620,15 @@ public Builder setUnitLabel(String unitLabel) {
   }
 
   public static class Tier {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The flat billing amount for an entire tier, regardless of the number of units in the tier.
      */
@@ -554,7 +646,8 @@ public static class Tier {
     @SerializedName("up_to")
     Object upTo;
 
-    private Tier(Long flatAmount, Long unitAmount, Object upTo) {
+    private Tier(Map<String, Object> extraParams, Long flatAmount, Long unitAmount, Object upTo) {
+      this.extraParams = extraParams;
       this.flatAmount = flatAmount;
       this.unitAmount = unitAmount;
       this.upTo = upTo;
@@ -565,6 +658,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long flatAmount;
 
       private Long unitAmount;
@@ -573,7 +668,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Tier build() {
-        return new Tier(this.flatAmount, this.unitAmount, this.upTo);
+        return new Tier(this.extraParams, this.flatAmount, this.unitAmount, this.upTo);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PlanCreateParams.Tier#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PlanCreateParams.Tier#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /**
@@ -627,12 +748,22 @@ public static class TransformUsage {
     @SerializedName("divide_by")
     Long divideBy;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** After division, either round the result `up` or `down`. */
     @SerializedName("round")
     Round round;
 
-    private TransformUsage(Long divideBy, Round round) {
+    private TransformUsage(Long divideBy, Map<String, Object> extraParams, Round round) {
       this.divideBy = divideBy;
+      this.extraParams = extraParams;
       this.round = round;
     }
 
@@ -643,11 +774,13 @@ public static Builder builder() {
     public static class Builder {
       private Long divideBy;
 
+      private Map<String, Object> extraParams;
+
       private Round round;
 
       /** Finalize and obtain parameter instance from this builder. */
       public TransformUsage build() {
-        return new TransformUsage(this.divideBy, this.round);
+        return new TransformUsage(this.divideBy, this.extraParams, this.round);
       }
 
       /** Divide usage by this number. */
@@ -656,6 +789,32 @@ public Builder setDivideBy(Long divideBy) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PlanCreateParams.TransformUsage#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PlanCreateParams.TransformUsage#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** After division, either round the result `up` or `down`. */
       public Builder setRound(Round round) {
         this.round = round;
diff --git a/src/main/java/com/stripe/param/PlanListParams.java b/src/main/java/com/stripe/param/PlanListParams.java
index 8751d14427b..a13b164ffc1 100644
--- a/src/main/java/com/stripe/param/PlanListParams.java
+++ b/src/main/java/com/stripe/param/PlanListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PlanListParams extends ApiRequestParams {
   /**
@@ -35,6 +37,15 @@ public class PlanListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -60,6 +71,7 @@ private PlanListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String product,
       String startingAfter) {
@@ -67,6 +79,7 @@ private PlanListParams(
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.product = product;
     this.startingAfter = startingAfter;
@@ -85,6 +98,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String product;
@@ -98,6 +113,7 @@ public PlanListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.product,
           this.startingAfter);
@@ -167,6 +183,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PlanListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PlanListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -195,6 +237,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -211,7 +262,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -223,6 +275,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -233,7 +287,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * PlanListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link PlanListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/PlanRetrieveParams.java b/src/main/java/com/stripe/param/PlanRetrieveParams.java
index fb97570b49e..b8743d9174e 100644
--- a/src/main/java/com/stripe/param/PlanRetrieveParams.java
+++ b/src/main/java/com/stripe/param/PlanRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class PlanRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private PlanRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private PlanRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public PlanRetrieveParams build() {
-      return new PlanRetrieveParams(this.expand);
+      return new PlanRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PlanRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PlanRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/PlanUpdateParams.java b/src/main/java/com/stripe/param/PlanUpdateParams.java
index 70f95a7be8e..cacd9277223 100644
--- a/src/main/java/com/stripe/param/PlanUpdateParams.java
+++ b/src/main/java/com/stripe/param/PlanUpdateParams.java
@@ -18,6 +18,15 @@ public class PlanUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to a plan object. It can be useful for storing
    * additional information about the plan in a structured format.
@@ -46,12 +55,14 @@ public class PlanUpdateParams extends ApiRequestParams {
   private PlanUpdateParams(
       Boolean active,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String nickname,
       String product,
       Long trialPeriodDays) {
     this.active = active;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.nickname = nickname;
     this.product = product;
@@ -67,6 +78,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String nickname;
@@ -80,6 +93,7 @@ public PlanUpdateParams build() {
       return new PlanUpdateParams(
           this.active,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.nickname,
           this.product,
@@ -118,6 +132,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * PlanUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link PlanUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/ProductCreateParams.java b/src/main/java/com/stripe/param/ProductCreateParams.java
index 1c14eefc230..dfbbf1e9d54 100644
--- a/src/main/java/com/stripe/param/ProductCreateParams.java
+++ b/src/main/java/com/stripe/param/ProductCreateParams.java
@@ -45,6 +45,15 @@ public class ProductCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * An identifier will be randomly generated by Stripe. You can optionally override this ID, but
    * the ID must be unique across all products in your Stripe account. Applicable to both `service`
@@ -124,6 +133,7 @@ private ProductCreateParams(
       List<String> deactivateOn,
       String description,
       List<String> expand,
+      Map<String, Object> extraParams,
       String id,
       List<String> images,
       Map<String, String> metadata,
@@ -140,6 +150,7 @@ private ProductCreateParams(
     this.deactivateOn = deactivateOn;
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.id = id;
     this.images = images;
     this.metadata = metadata;
@@ -169,6 +180,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String id;
 
     private List<String> images;
@@ -198,6 +211,7 @@ public ProductCreateParams build() {
           this.deactivateOn,
           this.description,
           this.expand,
+          this.extraParams,
           this.id,
           this.images,
           this.metadata,
@@ -312,6 +326,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ProductCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ProductCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * An identifier will be randomly generated by Stripe. You can optionally override this ID, but
      * the ID must be unique across all products in your Stripe account. Applicable to both
@@ -440,6 +480,15 @@ public Builder setUrl(String url) {
   }
 
   public static class PackageDimensions {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Height, in inches. Maximum precision is 2 decimal places. */
     @SerializedName("height")
     BigDecimal height;
@@ -457,7 +506,12 @@ public static class PackageDimensions {
     BigDecimal width;
 
     private PackageDimensions(
-        BigDecimal height, BigDecimal length, BigDecimal weight, BigDecimal width) {
+        Map<String, Object> extraParams,
+        BigDecimal height,
+        BigDecimal length,
+        BigDecimal weight,
+        BigDecimal width) {
+      this.extraParams = extraParams;
       this.height = height;
       this.length = length;
       this.weight = weight;
@@ -469,6 +523,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private BigDecimal height;
 
       private BigDecimal length;
@@ -479,7 +535,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public PackageDimensions build() {
-        return new PackageDimensions(this.height, this.length, this.weight, this.width);
+        return new PackageDimensions(
+            this.extraParams, this.height, this.length, this.weight, this.width);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ProductCreateParams.PackageDimensions#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ProductCreateParams.PackageDimensions#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Height, in inches. Maximum precision is 2 decimal places. */
diff --git a/src/main/java/com/stripe/param/ProductListParams.java b/src/main/java/com/stripe/param/ProductListParams.java
index 9546be42e08..5179d389824 100644
--- a/src/main/java/com/stripe/param/ProductListParams.java
+++ b/src/main/java/com/stripe/param/ProductListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class ProductListParams extends ApiRequestParams {
@@ -33,6 +35,15 @@ public class ProductListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Only return products with the given IDs. */
   @SerializedName("ids")
   List<String> ids;
@@ -70,6 +81,7 @@ private ProductListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       List<String> ids,
       Long limit,
       Boolean shippable,
@@ -80,6 +92,7 @@ private ProductListParams(
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.ids = ids;
     this.limit = limit;
     this.shippable = shippable;
@@ -101,6 +114,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<String> ids;
 
     private Long limit;
@@ -120,6 +135,7 @@ public ProductListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.ids,
           this.limit,
           this.shippable,
@@ -186,6 +202,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ProductListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ProductListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `ids` list. A list is initialized for the first `add/addAll` call, and
      * subsequent calls adds additional elements to the original list. See {@link
@@ -252,6 +294,15 @@ public Builder setUrl(String url) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -268,7 +319,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -280,6 +332,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -290,7 +344,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ProductListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ProductListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/ProductRetrieveParams.java b/src/main/java/com/stripe/param/ProductRetrieveParams.java
index a901e072903..8e50b6510d6 100644
--- a/src/main/java/com/stripe/param/ProductRetrieveParams.java
+++ b/src/main/java/com/stripe/param/ProductRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ProductRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ProductRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ProductRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ProductRetrieveParams build() {
-      return new ProductRetrieveParams(this.expand);
+      return new ProductRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ProductRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ProductRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/ProductUpdateParams.java b/src/main/java/com/stripe/param/ProductUpdateParams.java
index 554d40f0a72..98fc05a4978 100644
--- a/src/main/java/com/stripe/param/ProductUpdateParams.java
+++ b/src/main/java/com/stripe/param/ProductUpdateParams.java
@@ -44,6 +44,15 @@ public class ProductUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** A list of up to 8 URLs of images for this product, meant to be displayable to the customer. */
   @SerializedName("images")
   Object images;
@@ -101,6 +110,7 @@ private ProductUpdateParams(
       List<String> deactivateOn,
       String description,
       List<String> expand,
+      Map<String, Object> extraParams,
       Object images,
       Map<String, String> metadata,
       String name,
@@ -115,6 +125,7 @@ private ProductUpdateParams(
     this.deactivateOn = deactivateOn;
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.images = images;
     this.metadata = metadata;
     this.name = name;
@@ -142,6 +153,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Object images;
 
     private Map<String, String> metadata;
@@ -167,6 +180,7 @@ public ProductUpdateParams build() {
           this.deactivateOn,
           this.description,
           this.expand,
+          this.extraParams,
           this.images,
           this.metadata,
           this.name,
@@ -269,6 +283,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ProductUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ProductUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A list of up to 8 URLs of images for this product, meant to be displayable to the customer.
      */
@@ -374,6 +414,15 @@ public Builder setUrl(String url) {
   }
 
   public static class PackageDimensions {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Height, in inches. Maximum precision is 2 decimal places. */
     @SerializedName("height")
     BigDecimal height;
@@ -391,7 +440,12 @@ public static class PackageDimensions {
     BigDecimal width;
 
     private PackageDimensions(
-        BigDecimal height, BigDecimal length, BigDecimal weight, BigDecimal width) {
+        Map<String, Object> extraParams,
+        BigDecimal height,
+        BigDecimal length,
+        BigDecimal weight,
+        BigDecimal width) {
+      this.extraParams = extraParams;
       this.height = height;
       this.length = length;
       this.weight = weight;
@@ -403,6 +457,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private BigDecimal height;
 
       private BigDecimal length;
@@ -413,7 +469,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public PackageDimensions build() {
-        return new PackageDimensions(this.height, this.length, this.weight, this.width);
+        return new PackageDimensions(
+            this.extraParams, this.height, this.length, this.weight, this.width);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ProductUpdateParams.PackageDimensions#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ProductUpdateParams.PackageDimensions#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Height, in inches. Maximum precision is 2 decimal places. */
diff --git a/src/main/java/com/stripe/param/RecipientCreateParams.java b/src/main/java/com/stripe/param/RecipientCreateParams.java
index 6f57f98e3e1..3a97e4c09b9 100644
--- a/src/main/java/com/stripe/param/RecipientCreateParams.java
+++ b/src/main/java/com/stripe/param/RecipientCreateParams.java
@@ -46,6 +46,15 @@ public class RecipientCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -79,6 +88,7 @@ private RecipientCreateParams(
       String description,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String name,
       String taxId,
@@ -88,6 +98,7 @@ private RecipientCreateParams(
     this.description = description;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.name = name;
     this.taxId = taxId;
@@ -109,6 +120,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String name;
@@ -125,6 +138,7 @@ public RecipientCreateParams build() {
           this.description,
           this.email,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.name,
           this.taxId,
@@ -197,6 +211,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RecipientCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RecipientCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/RecipientListParams.java b/src/main/java/com/stripe/param/RecipientListParams.java
index eecb3b7bd20..03068167c80 100644
--- a/src/main/java/com/stripe/param/RecipientListParams.java
+++ b/src/main/java/com/stripe/param/RecipientListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class RecipientListParams extends ApiRequestParams {
@@ -25,6 +27,15 @@ public class RecipientListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -52,6 +63,7 @@ private RecipientListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       Type type,
@@ -59,6 +71,7 @@ private RecipientListParams(
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.type = type;
@@ -76,6 +89,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -90,6 +105,7 @@ public RecipientListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter,
           this.type,
@@ -143,6 +159,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RecipientListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RecipientListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -176,6 +218,15 @@ public Builder setVerified(Boolean verified) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -192,7 +243,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -204,6 +256,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -214,7 +268,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * RecipientListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link RecipientListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/RecipientRetrieveParams.java b/src/main/java/com/stripe/param/RecipientRetrieveParams.java
index dca5ced43c5..92b20c70871 100644
--- a/src/main/java/com/stripe/param/RecipientRetrieveParams.java
+++ b/src/main/java/com/stripe/param/RecipientRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class RecipientRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private RecipientRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private RecipientRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public RecipientRetrieveParams build() {
-      return new RecipientRetrieveParams(this.expand);
+      return new RecipientRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RecipientRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RecipientRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/RecipientUpdateParams.java b/src/main/java/com/stripe/param/RecipientUpdateParams.java
index a517e6c057d..6b54e3dc0bc 100644
--- a/src/main/java/com/stripe/param/RecipientUpdateParams.java
+++ b/src/main/java/com/stripe/param/RecipientUpdateParams.java
@@ -52,6 +52,15 @@ public class RecipientUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -82,6 +91,7 @@ private RecipientUpdateParams(
       String description,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String name,
       String taxId) {
@@ -91,6 +101,7 @@ private RecipientUpdateParams(
     this.description = description;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.name = name;
     this.taxId = taxId;
@@ -113,6 +124,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String name;
@@ -128,6 +141,7 @@ public RecipientUpdateParams build() {
           this.description,
           this.email,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.name,
           this.taxId);
@@ -208,6 +222,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RecipientUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RecipientUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/RefundCollectionListParams.java b/src/main/java/com/stripe/param/RefundCollectionListParams.java
index f7691035219..b137abcf339 100644
--- a/src/main/java/com/stripe/param/RefundCollectionListParams.java
+++ b/src/main/java/com/stripe/param/RefundCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class RefundCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class RefundCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class RefundCollectionListParams extends ApiRequestParams {
   String startingAfter;
 
   private RefundCollectionListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public RefundCollectionListParams build() {
       return new RefundCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RefundCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RefundCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/RefundCollectionRetrieveParams.java b/src/main/java/com/stripe/param/RefundCollectionRetrieveParams.java
index 9663423cd69..c9cbe118439 100644
--- a/src/main/java/com/stripe/param/RefundCollectionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/RefundCollectionRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class RefundCollectionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private RefundCollectionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private RefundCollectionRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public RefundCollectionRetrieveParams build() {
-      return new RefundCollectionRetrieveParams(this.expand);
+      return new RefundCollectionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RefundCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RefundCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/RefundCreateParams.java b/src/main/java/com/stripe/param/RefundCreateParams.java
index e2c8ccc70fd..9d839ac1b5c 100644
--- a/src/main/java/com/stripe/param/RefundCreateParams.java
+++ b/src/main/java/com/stripe/param/RefundCreateParams.java
@@ -21,6 +21,15 @@ public class RefundCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
@@ -37,6 +46,7 @@ private RefundCreateParams(
       Long amount,
       String charge,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       Reason reason,
       Boolean refundApplicationFee,
@@ -44,6 +54,7 @@ private RefundCreateParams(
     this.amount = amount;
     this.charge = charge;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.reason = reason;
     this.refundApplicationFee = refundApplicationFee;
@@ -61,6 +72,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private Reason reason;
@@ -75,6 +88,7 @@ public RefundCreateParams build() {
           this.amount,
           this.charge,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.reason,
           this.refundApplicationFee,
@@ -117,6 +131,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RefundCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RefundCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/RefundListParams.java b/src/main/java/com/stripe/param/RefundListParams.java
index b4b27b10039..96799800964 100644
--- a/src/main/java/com/stripe/param/RefundListParams.java
+++ b/src/main/java/com/stripe/param/RefundListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class RefundListParams extends ApiRequestParams {
   /** Only return refunds for the charge specified by this charge ID. */
@@ -28,6 +30,15 @@ public class RefundListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -49,12 +60,14 @@ private RefundListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter) {
     this.charge = charge;
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -72,6 +85,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -83,6 +98,7 @@ public RefundListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter);
     }
@@ -140,6 +156,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RefundListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RefundListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -162,6 +204,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -178,7 +229,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -190,6 +242,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -200,7 +254,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * RefundListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link RefundListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/RefundRetrieveParams.java b/src/main/java/com/stripe/param/RefundRetrieveParams.java
index 31092f26242..46eeea8288c 100644
--- a/src/main/java/com/stripe/param/RefundRetrieveParams.java
+++ b/src/main/java/com/stripe/param/RefundRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class RefundRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private RefundRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private RefundRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public RefundRetrieveParams build() {
-      return new RefundRetrieveParams(this.expand);
+      return new RefundRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RefundRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RefundRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/RefundUpdateParams.java b/src/main/java/com/stripe/param/RefundUpdateParams.java
index 31c8c1b77da..4fe60725978 100644
--- a/src/main/java/com/stripe/param/RefundUpdateParams.java
+++ b/src/main/java/com/stripe/param/RefundUpdateParams.java
@@ -14,6 +14,15 @@ public class RefundUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -22,8 +31,10 @@ public class RefundUpdateParams extends ApiRequestParams {
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private RefundUpdateParams(List<String> expand, Map<String, String> metadata) {
+  private RefundUpdateParams(
+      List<String> expand, Map<String, Object> extraParams, Map<String, String> metadata) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -34,11 +45,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public RefundUpdateParams build() {
-      return new RefundUpdateParams(this.expand, this.metadata);
+      return new RefundUpdateParams(this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -67,6 +80,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * RefundUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link RefundUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/ReviewApproveParams.java b/src/main/java/com/stripe/param/ReviewApproveParams.java
index bfddccfc3ce..91aa606b77d 100644
--- a/src/main/java/com/stripe/param/ReviewApproveParams.java
+++ b/src/main/java/com/stripe/param/ReviewApproveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReviewApproveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ReviewApproveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ReviewApproveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ReviewApproveParams build() {
-      return new ReviewApproveParams(this.expand);
+      return new ReviewApproveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReviewApproveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReviewApproveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/ReviewListParams.java b/src/main/java/com/stripe/param/ReviewListParams.java
index 55aca4e9b96..7067608fc0a 100644
--- a/src/main/java/com/stripe/param/ReviewListParams.java
+++ b/src/main/java/com/stripe/param/ReviewListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReviewListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -24,6 +26,15 @@ public class ReviewListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -41,10 +52,16 @@ public class ReviewListParams extends ApiRequestParams {
   String startingAfter;
 
   private ReviewListParams(
-      Object created, String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      Object created,
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -60,6 +77,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -67,7 +86,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public ReviewListParams build() {
       return new ReviewListParams(
-          this.created, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.created,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     public Builder setCreated(Created created) {
@@ -117,6 +141,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReviewListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReviewListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -139,6 +189,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -155,7 +214,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -167,6 +227,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -177,7 +239,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ReviewListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ReviewListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/ReviewRetrieveParams.java b/src/main/java/com/stripe/param/ReviewRetrieveParams.java
index 1fce2daede6..49de5a8b474 100644
--- a/src/main/java/com/stripe/param/ReviewRetrieveParams.java
+++ b/src/main/java/com/stripe/param/ReviewRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReviewRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ReviewRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ReviewRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ReviewRetrieveParams build() {
-      return new ReviewRetrieveParams(this.expand);
+      return new ReviewRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReviewRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReviewRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/SkuCreateParams.java b/src/main/java/com/stripe/param/SkuCreateParams.java
index 6ff7b9680c0..e82c0efc1fa 100644
--- a/src/main/java/com/stripe/param/SkuCreateParams.java
+++ b/src/main/java/com/stripe/param/SkuCreateParams.java
@@ -36,6 +36,15 @@ public class SkuCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * The identifier for the SKU. Must be unique. If not provided, an identifier will be randomly
    * generated.
@@ -78,6 +87,7 @@ private SkuCreateParams(
       Map<String, String> attributes,
       String currency,
       List<String> expand,
+      Map<String, Object> extraParams,
       String id,
       String image,
       Inventory inventory,
@@ -89,6 +99,7 @@ private SkuCreateParams(
     this.attributes = attributes;
     this.currency = currency;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.id = id;
     this.image = image;
     this.inventory = inventory;
@@ -111,6 +122,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String id;
 
     private String image;
@@ -132,6 +145,7 @@ public SkuCreateParams build() {
           this.attributes,
           this.currency,
           this.expand,
+          this.extraParams,
           this.id,
           this.image,
           this.inventory,
@@ -208,6 +222,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SkuCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SkuCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * The identifier for the SKU. Must be unique. If not provided, an identifier will be randomly
      * generated.
@@ -278,6 +318,15 @@ public Builder setProduct(String product) {
   }
 
   public static class Inventory {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The count of inventory available. Required if `type` is `finite`. */
     @SerializedName("quantity")
     Long quantity;
@@ -293,7 +342,12 @@ public static class Inventory {
     @SerializedName("value")
     ApiRequestParams.EnumParam value;
 
-    private Inventory(Long quantity, Type type, ApiRequestParams.EnumParam value) {
+    private Inventory(
+        Map<String, Object> extraParams,
+        Long quantity,
+        Type type,
+        ApiRequestParams.EnumParam value) {
+      this.extraParams = extraParams;
       this.quantity = quantity;
       this.type = type;
       this.value = value;
@@ -304,6 +358,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long quantity;
 
       private Type type;
@@ -312,7 +368,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Inventory build() {
-        return new Inventory(this.quantity, this.type, this.value);
+        return new Inventory(this.extraParams, this.quantity, this.type, this.value);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SkuCreateParams.Inventory#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SkuCreateParams.Inventory#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** The count of inventory available. Required if `type` is `finite`. */
@@ -386,6 +468,15 @@ public enum Value implements ApiRequestParams.EnumParam {
   }
 
   public static class PackageDimensions {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Height, in inches. Maximum precision is 2 decimal places. */
     @SerializedName("height")
     BigDecimal height;
@@ -403,7 +494,12 @@ public static class PackageDimensions {
     BigDecimal width;
 
     private PackageDimensions(
-        BigDecimal height, BigDecimal length, BigDecimal weight, BigDecimal width) {
+        Map<String, Object> extraParams,
+        BigDecimal height,
+        BigDecimal length,
+        BigDecimal weight,
+        BigDecimal width) {
+      this.extraParams = extraParams;
       this.height = height;
       this.length = length;
       this.weight = weight;
@@ -415,6 +511,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private BigDecimal height;
 
       private BigDecimal length;
@@ -425,7 +523,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public PackageDimensions build() {
-        return new PackageDimensions(this.height, this.length, this.weight, this.width);
+        return new PackageDimensions(
+            this.extraParams, this.height, this.length, this.weight, this.width);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SkuCreateParams.PackageDimensions#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SkuCreateParams.PackageDimensions#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Height, in inches. Maximum precision is 2 decimal places. */
diff --git a/src/main/java/com/stripe/param/SkuListParams.java b/src/main/java/com/stripe/param/SkuListParams.java
index 6ff9f466d51..8eee8011d0f 100644
--- a/src/main/java/com/stripe/param/SkuListParams.java
+++ b/src/main/java/com/stripe/param/SkuListParams.java
@@ -39,6 +39,15 @@ public class SkuListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Only return SKUs with the given IDs. */
   @SerializedName("ids")
   List<String> ids;
@@ -75,6 +84,7 @@ private SkuListParams(
       Map<String, String> attributes,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       List<String> ids,
       Boolean inStock,
       Long limit,
@@ -84,6 +94,7 @@ private SkuListParams(
     this.attributes = attributes;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.ids = ids;
     this.inStock = inStock;
     this.limit = limit;
@@ -104,6 +115,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<String> ids;
 
     private Boolean inStock;
@@ -121,6 +134,7 @@ public SkuListParams build() {
           this.attributes,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.ids,
           this.inStock,
           this.limit,
@@ -200,6 +214,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SkuListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SkuListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `ids` list. A list is initialized for the first `add/addAll` call, and
      * subsequent calls adds additional elements to the original list. See {@link SkuListParams#ids}
diff --git a/src/main/java/com/stripe/param/SkuRetrieveParams.java b/src/main/java/com/stripe/param/SkuRetrieveParams.java
index 754294094d3..a7ded91a13a 100644
--- a/src/main/java/com/stripe/param/SkuRetrieveParams.java
+++ b/src/main/java/com/stripe/param/SkuRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SkuRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private SkuRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private SkuRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public SkuRetrieveParams build() {
-      return new SkuRetrieveParams(this.expand);
+      return new SkuRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SkuRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SkuRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/SkuUpdateParams.java b/src/main/java/com/stripe/param/SkuUpdateParams.java
index 87b92f24afd..f6da34c8df0 100644
--- a/src/main/java/com/stripe/param/SkuUpdateParams.java
+++ b/src/main/java/com/stripe/param/SkuUpdateParams.java
@@ -37,6 +37,15 @@ public class SkuUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The URL of an image for this SKU, meant to be displayable to the customer. */
   @SerializedName("image")
   String image;
@@ -75,6 +84,7 @@ private SkuUpdateParams(
       Map<String, String> attributes,
       String currency,
       List<String> expand,
+      Map<String, Object> extraParams,
       String image,
       Inventory inventory,
       Map<String, String> metadata,
@@ -85,6 +95,7 @@ private SkuUpdateParams(
     this.attributes = attributes;
     this.currency = currency;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.image = image;
     this.inventory = inventory;
     this.metadata = metadata;
@@ -106,6 +117,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String image;
 
     private Inventory inventory;
@@ -125,6 +138,7 @@ public SkuUpdateParams build() {
           this.attributes,
           this.currency,
           this.expand,
+          this.extraParams,
           this.image,
           this.inventory,
           this.metadata,
@@ -200,6 +214,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SkuUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SkuUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The URL of an image for this SKU, meant to be displayable to the customer. */
     public Builder setImage(String image) {
       this.image = image;
@@ -270,6 +310,15 @@ public Builder setProduct(String product) {
   }
 
   public static class Inventory {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The count of inventory available. Required if `type` is `finite`. */
     @SerializedName("quantity")
     Long quantity;
@@ -285,7 +334,12 @@ public static class Inventory {
     @SerializedName("value")
     ApiRequestParams.EnumParam value;
 
-    private Inventory(Long quantity, Type type, ApiRequestParams.EnumParam value) {
+    private Inventory(
+        Map<String, Object> extraParams,
+        Long quantity,
+        Type type,
+        ApiRequestParams.EnumParam value) {
+      this.extraParams = extraParams;
       this.quantity = quantity;
       this.type = type;
       this.value = value;
@@ -296,6 +350,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long quantity;
 
       private Type type;
@@ -304,7 +360,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Inventory build() {
-        return new Inventory(this.quantity, this.type, this.value);
+        return new Inventory(this.extraParams, this.quantity, this.type, this.value);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SkuUpdateParams.Inventory#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SkuUpdateParams.Inventory#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** The count of inventory available. Required if `type` is `finite`. */
@@ -378,6 +460,15 @@ public enum Value implements ApiRequestParams.EnumParam {
   }
 
   public static class PackageDimensions {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Height, in inches. Maximum precision is 2 decimal places. */
     @SerializedName("height")
     BigDecimal height;
@@ -395,7 +486,12 @@ public static class PackageDimensions {
     BigDecimal width;
 
     private PackageDimensions(
-        BigDecimal height, BigDecimal length, BigDecimal weight, BigDecimal width) {
+        Map<String, Object> extraParams,
+        BigDecimal height,
+        BigDecimal length,
+        BigDecimal weight,
+        BigDecimal width) {
+      this.extraParams = extraParams;
       this.height = height;
       this.length = length;
       this.weight = weight;
@@ -407,6 +503,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private BigDecimal height;
 
       private BigDecimal length;
@@ -417,7 +515,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public PackageDimensions build() {
-        return new PackageDimensions(this.height, this.length, this.weight, this.width);
+        return new PackageDimensions(
+            this.extraParams, this.height, this.length, this.weight, this.width);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SkuUpdateParams.PackageDimensions#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SkuUpdateParams.PackageDimensions#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Height, in inches. Maximum precision is 2 decimal places. */
diff --git a/src/main/java/com/stripe/param/SourceCreateParams.java b/src/main/java/com/stripe/param/SourceCreateParams.java
index e7d2d5c97a1..0f29de18204 100644
--- a/src/main/java/com/stripe/param/SourceCreateParams.java
+++ b/src/main/java/com/stripe/param/SourceCreateParams.java
@@ -36,6 +36,15 @@ public class SourceCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * The authentication `flow` of the source to create. `flow` is one of `redirect`, `receiver`,
    * `code_verification`, `none`. It is generally inferred unless a type supports multiple flows.
@@ -107,6 +116,7 @@ private SourceCreateParams(
       String currency,
       String customer,
       List<String> expand,
+      Map<String, Object> extraParams,
       Flow flow,
       Map<String, String> metadata,
       String originalSource,
@@ -121,6 +131,7 @@ private SourceCreateParams(
     this.currency = currency;
     this.customer = customer;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.flow = flow;
     this.metadata = metadata;
     this.originalSource = originalSource;
@@ -146,6 +157,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Flow flow;
 
     private Map<String, String> metadata;
@@ -173,6 +186,7 @@ public SourceCreateParams build() {
           this.currency,
           this.customer,
           this.expand,
+          this.extraParams,
           this.flow,
           this.metadata,
           this.originalSource,
@@ -238,6 +252,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SourceCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SourceCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * The authentication `flow` of the source to create. `flow` is one of `redirect`, `receiver`,
      * `code_verification`, `none`. It is generally inferred unless a type supports multiple flows.
@@ -351,6 +391,15 @@ public static class Owner {
     @SerializedName("email")
     String email;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Owner's full name. */
     @SerializedName("name")
     String name;
@@ -359,9 +408,11 @@ public static class Owner {
     @SerializedName("phone")
     String phone;
 
-    private Owner(Address address, String email, String name, String phone) {
+    private Owner(
+        Address address, String email, Map<String, Object> extraParams, String name, String phone) {
       this.address = address;
       this.email = email;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
     }
@@ -375,13 +426,15 @@ public static class Builder {
 
       private String email;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Owner build() {
-        return new Owner(this.address, this.email, this.name, this.phone);
+        return new Owner(this.address, this.email, this.extraParams, this.name, this.phone);
       }
 
       /** Owner's address. */
@@ -396,6 +449,32 @@ public Builder setEmail(String email) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SourceCreateParams.Owner#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SourceCreateParams.Owner#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Owner's full name. */
       public Builder setName(String name) {
         this.name = name;
@@ -416,6 +495,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -431,12 +519,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -452,6 +542,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -463,7 +555,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -476,6 +574,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SourceCreateParams.Owner.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SourceCreateParams.Owner.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
@@ -500,6 +626,15 @@ public Builder setState(String state) {
   }
 
   public static class Receiver {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The method Stripe should use to request information needed to process a refund or mispayment.
      * Either `email` (an email is sent directly to the customer) or `manual` (a
@@ -509,7 +644,9 @@ public static class Receiver {
     @SerializedName("refund_attributes_method")
     RefundAttributesMethod refundAttributesMethod;
 
-    private Receiver(RefundAttributesMethod refundAttributesMethod) {
+    private Receiver(
+        Map<String, Object> extraParams, RefundAttributesMethod refundAttributesMethod) {
+      this.extraParams = extraParams;
       this.refundAttributesMethod = refundAttributesMethod;
     }
 
@@ -518,11 +655,39 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private RefundAttributesMethod refundAttributesMethod;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Receiver build() {
-        return new Receiver(this.refundAttributesMethod);
+        return new Receiver(this.extraParams, this.refundAttributesMethod);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SourceCreateParams.Receiver#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SourceCreateParams.Receiver#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /**
@@ -557,6 +722,15 @@ public enum RefundAttributesMethod implements ApiRequestParams.EnumParam {
   }
 
   public static class Redirect {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The URL you provide to redirect the customer back to you after they authenticated their
      * payment. It can use your application URI scheme in the context of a mobile application.
@@ -564,7 +738,8 @@ public static class Redirect {
     @SerializedName("return_url")
     String returnUrl;
 
-    private Redirect(String returnUrl) {
+    private Redirect(Map<String, Object> extraParams, String returnUrl) {
+      this.extraParams = extraParams;
       this.returnUrl = returnUrl;
     }
 
@@ -573,11 +748,39 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String returnUrl;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Redirect build() {
-        return new Redirect(this.returnUrl);
+        return new Redirect(this.extraParams, this.returnUrl);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SourceCreateParams.Redirect#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SourceCreateParams.Redirect#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /**
diff --git a/src/main/java/com/stripe/param/SourceRetrieveParams.java b/src/main/java/com/stripe/param/SourceRetrieveParams.java
index 32d894df8f9..2fe466431ce 100644
--- a/src/main/java/com/stripe/param/SourceRetrieveParams.java
+++ b/src/main/java/com/stripe/param/SourceRetrieveParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SourceRetrieveParams extends ApiRequestParams {
   /**
@@ -18,9 +20,20 @@ public class SourceRetrieveParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
-  private SourceRetrieveParams(String clientSecret, List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private SourceRetrieveParams(
+      String clientSecret, List<String> expand, Map<String, Object> extraParams) {
     this.clientSecret = clientSecret;
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -32,9 +45,11 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public SourceRetrieveParams build() {
-      return new SourceRetrieveParams(this.clientSecret, this.expand);
+      return new SourceRetrieveParams(this.clientSecret, this.expand, this.extraParams);
     }
 
     /**
@@ -71,5 +86,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SourceRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SourceRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/SourceSourceTransactionsParams.java b/src/main/java/com/stripe/param/SourceSourceTransactionsParams.java
index 431c16ee58c..ea872bcb040 100644
--- a/src/main/java/com/stripe/param/SourceSourceTransactionsParams.java
+++ b/src/main/java/com/stripe/param/SourceSourceTransactionsParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SourceSourceTransactionsParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class SourceSourceTransactionsParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class SourceSourceTransactionsParams extends ApiRequestParams {
   String startingAfter;
 
   private SourceSourceTransactionsParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public SourceSourceTransactionsParams build() {
       return new SourceSourceTransactionsParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SourceSourceTransactionsParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SourceSourceTransactionsParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/SourceUpdateParams.java b/src/main/java/com/stripe/param/SourceUpdateParams.java
index 3d353dc75c5..d6d5b62b752 100644
--- a/src/main/java/com/stripe/param/SourceUpdateParams.java
+++ b/src/main/java/com/stripe/param/SourceUpdateParams.java
@@ -14,6 +14,15 @@ public class SourceUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A set of key-value pairs that you can attach to a source object. It can be useful for storing
    * additional information about the source in a structured format.
@@ -28,8 +37,13 @@ public class SourceUpdateParams extends ApiRequestParams {
   @SerializedName("owner")
   Owner owner;
 
-  private SourceUpdateParams(List<String> expand, Map<String, String> metadata, Owner owner) {
+  private SourceUpdateParams(
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata,
+      Owner owner) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.owner = owner;
   }
@@ -41,13 +55,15 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private Owner owner;
 
     /** Finalize and obtain parameter instance from this builder. */
     public SourceUpdateParams build() {
-      return new SourceUpdateParams(this.expand, this.metadata, this.owner);
+      return new SourceUpdateParams(this.expand, this.extraParams, this.metadata, this.owner);
     }
 
     /**
@@ -76,6 +92,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SourceUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SourceUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -121,6 +163,15 @@ public static class Owner {
     @SerializedName("email")
     String email;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Owner's full name. */
     @SerializedName("name")
     String name;
@@ -129,9 +180,11 @@ public static class Owner {
     @SerializedName("phone")
     String phone;
 
-    private Owner(Address address, String email, String name, String phone) {
+    private Owner(
+        Address address, String email, Map<String, Object> extraParams, String name, String phone) {
       this.address = address;
       this.email = email;
+      this.extraParams = extraParams;
       this.name = name;
       this.phone = phone;
     }
@@ -145,13 +198,15 @@ public static class Builder {
 
       private String email;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String phone;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Owner build() {
-        return new Owner(this.address, this.email, this.name, this.phone);
+        return new Owner(this.address, this.email, this.extraParams, this.name, this.phone);
       }
 
       /** Owner's address. */
@@ -166,6 +221,32 @@ public Builder setEmail(String email) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SourceUpdateParams.Owner#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SourceUpdateParams.Owner#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Owner's full name. */
       public Builder setName(String name) {
         this.name = name;
@@ -186,6 +267,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -201,12 +291,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -222,6 +314,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -233,7 +327,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -246,6 +346,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SourceUpdateParams.Owner.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SourceUpdateParams.Owner.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
diff --git a/src/main/java/com/stripe/param/SourceVerifyParams.java b/src/main/java/com/stripe/param/SourceVerifyParams.java
index b6a518778ac..65a20d33d93 100644
--- a/src/main/java/com/stripe/param/SourceVerifyParams.java
+++ b/src/main/java/com/stripe/param/SourceVerifyParams.java
@@ -5,19 +5,32 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SourceVerifyParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The values needed to verify the source. */
   @SerializedName("values")
   List<String> values;
 
-  private SourceVerifyParams(List<String> expand, List<String> values) {
+  private SourceVerifyParams(
+      List<String> expand, Map<String, Object> extraParams, List<String> values) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.values = values;
   }
 
@@ -28,11 +41,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<String> values;
 
     /** Finalize and obtain parameter instance from this builder. */
     public SourceVerifyParams build() {
-      return new SourceVerifyParams(this.expand, this.values);
+      return new SourceVerifyParams(this.expand, this.extraParams, this.values);
     }
 
     /**
@@ -61,6 +76,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SourceVerifyParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SourceVerifyParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `values` list. A list is initialized for the first `add/addAll` call, and
      * subsequent calls adds additional elements to the original list. See {@link
diff --git a/src/main/java/com/stripe/param/SubscriptionCancelParams.java b/src/main/java/com/stripe/param/SubscriptionCancelParams.java
index 97eeccf3c1c..90a3cb9959b 100644
--- a/src/main/java/com/stripe/param/SubscriptionCancelParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionCancelParams.java
@@ -4,8 +4,19 @@
 
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
+import java.util.HashMap;
+import java.util.Map;
 
 public class SubscriptionCancelParams extends ApiRequestParams {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Will generate a final invoice that invoices for any un-invoiced metered usage and new/pending
    * proration invoice items.
@@ -20,7 +31,9 @@ public class SubscriptionCancelParams extends ApiRequestParams {
   @SerializedName("prorate")
   Boolean prorate;
 
-  private SubscriptionCancelParams(Boolean invoiceNow, Boolean prorate) {
+  private SubscriptionCancelParams(
+      Map<String, Object> extraParams, Boolean invoiceNow, Boolean prorate) {
+    this.extraParams = extraParams;
     this.invoiceNow = invoiceNow;
     this.prorate = prorate;
   }
@@ -30,13 +43,41 @@ public static Builder builder() {
   }
 
   public static class Builder {
+    private Map<String, Object> extraParams;
+
     private Boolean invoiceNow;
 
     private Boolean prorate;
 
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionCancelParams build() {
-      return new SubscriptionCancelParams(this.invoiceNow, this.prorate);
+      return new SubscriptionCancelParams(this.extraParams, this.invoiceNow, this.prorate);
+    }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
     }
 
     /**
diff --git a/src/main/java/com/stripe/param/SubscriptionCreateParams.java b/src/main/java/com/stripe/param/SubscriptionCreateParams.java
index cc9cfdd70c6..4e0cfebef20 100644
--- a/src/main/java/com/stripe/param/SubscriptionCreateParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionCreateParams.java
@@ -114,6 +114,15 @@ public class SubscriptionCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** List of subscription items, each with an attached plan. */
   @SerializedName("items")
   List<Item> items;
@@ -195,6 +204,7 @@ private SubscriptionCreateParams(
       String defaultSource,
       Object defaultTaxRates,
       List<String> expand,
+      Map<String, Object> extraParams,
       List<Item> items,
       Map<String, String> metadata,
       Boolean prorate,
@@ -217,6 +227,7 @@ private SubscriptionCreateParams(
     this.defaultSource = defaultSource;
     this.defaultTaxRates = defaultTaxRates;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.items = items;
     this.metadata = metadata;
     this.prorate = prorate;
@@ -260,6 +271,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<Item> items;
 
     private Map<String, String> metadata;
@@ -293,6 +306,7 @@ public SubscriptionCreateParams build() {
           this.defaultSource,
           this.defaultTaxRates,
           this.expand,
+          this.extraParams,
           this.items,
           this.metadata,
           this.prorate,
@@ -470,6 +484,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `items` list. A list is initialized for the first `add/addAll` call, and
      * subsequent calls adds additional elements to the original list. See {@link
@@ -621,6 +661,15 @@ public static class BillingThresholds {
     @SerializedName("amount_gte")
     Long amountGte;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Indicates if the `billing_cycle_anchor` should be reset when a threshold is reached. If true,
      * `billing_cycle_anchor` will be updated to the date/time the threshold was last reached;
@@ -629,8 +678,10 @@ public static class BillingThresholds {
     @SerializedName("reset_billing_cycle_anchor")
     Boolean resetBillingCycleAnchor;
 
-    private BillingThresholds(Long amountGte, Boolean resetBillingCycleAnchor) {
+    private BillingThresholds(
+        Long amountGte, Map<String, Object> extraParams, Boolean resetBillingCycleAnchor) {
       this.amountGte = amountGte;
+      this.extraParams = extraParams;
       this.resetBillingCycleAnchor = resetBillingCycleAnchor;
     }
 
@@ -641,11 +692,14 @@ public static Builder builder() {
     public static class Builder {
       private Long amountGte;
 
+      private Map<String, Object> extraParams;
+
       private Boolean resetBillingCycleAnchor;
 
       /** Finalize and obtain parameter instance from this builder. */
       public BillingThresholds build() {
-        return new BillingThresholds(this.amountGte, this.resetBillingCycleAnchor);
+        return new BillingThresholds(
+            this.amountGte, this.extraParams, this.resetBillingCycleAnchor);
       }
 
       /** Monetary threshold that triggers the subscription to advance to a new billing period. */
@@ -654,6 +708,33 @@ public Builder setAmountGte(Long amountGte) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionCreateParams.BillingThresholds#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionCreateParams.BillingThresholds#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Indicates if the `billing_cycle_anchor` should be reset when a threshold is reached. If
        * true, `billing_cycle_anchor` will be updated to the date/time the threshold was last
@@ -674,6 +755,15 @@ public static class Item {
     @SerializedName("billing_thresholds")
     Object billingThresholds;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Set of key-value pairs that you can attach to an object. This can be useful for storing
      * additional information about the object in a structured format.
@@ -698,11 +788,13 @@ public static class Item {
 
     private Item(
         Object billingThresholds,
+        Map<String, Object> extraParams,
         Map<String, String> metadata,
         String plan,
         Long quantity,
         Object taxRates) {
       this.billingThresholds = billingThresholds;
+      this.extraParams = extraParams;
       this.metadata = metadata;
       this.plan = plan;
       this.quantity = quantity;
@@ -716,6 +808,8 @@ public static Builder builder() {
     public static class Builder {
       private Object billingThresholds;
 
+      private Map<String, Object> extraParams;
+
       private Map<String, String> metadata;
 
       private String plan;
@@ -727,7 +821,12 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Item build() {
         return new Item(
-            this.billingThresholds, this.metadata, this.plan, this.quantity, this.taxRates);
+            this.billingThresholds,
+            this.extraParams,
+            this.metadata,
+            this.plan,
+            this.quantity,
+            this.taxRates);
       }
 
       /**
@@ -748,6 +847,32 @@ public Builder setBillingThresholds(EmptyParam billingThresholds) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionCreateParams.Item#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionCreateParams.Item#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll`
        * call, and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -806,11 +931,21 @@ public Builder setTaxRates(List<String> taxRates) {
     }
 
     public static class BillingThresholds {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Usage threshold that triggers the subscription to advance to a new billing period. */
       @SerializedName("usage_gte")
       Long usageGte;
 
-      private BillingThresholds(Long usageGte) {
+      private BillingThresholds(Map<String, Object> extraParams, Long usageGte) {
+        this.extraParams = extraParams;
         this.usageGte = usageGte;
       }
 
@@ -819,11 +954,41 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private Long usageGte;
 
         /** Finalize and obtain parameter instance from this builder. */
         public BillingThresholds build() {
-          return new BillingThresholds(this.usageGte);
+          return new BillingThresholds(this.extraParams, this.usageGte);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SubscriptionCreateParams.Item.BillingThresholds#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SubscriptionCreateParams.Item.BillingThresholds#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** Usage threshold that triggers the subscription to advance to a new billing period. */
@@ -840,8 +1005,18 @@ public static class TransferData {
     @SerializedName("destination")
     String destination;
 
-    private TransferData(String destination) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private TransferData(String destination, Map<String, Object> extraParams) {
       this.destination = destination;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -851,9 +1026,11 @@ public static Builder builder() {
     public static class Builder {
       private String destination;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public TransferData build() {
-        return new TransferData(this.destination);
+        return new TransferData(this.destination, this.extraParams);
       }
 
       /** ID of an existing, connected Stripe account. */
@@ -861,6 +1038,32 @@ public Builder setDestination(String destination) {
         this.destination = destination;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionCreateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionCreateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 
diff --git a/src/main/java/com/stripe/param/SubscriptionItemCreateParams.java b/src/main/java/com/stripe/param/SubscriptionItemCreateParams.java
index 692b16fa82e..5288f2e1867 100644
--- a/src/main/java/com/stripe/param/SubscriptionItemCreateParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionItemCreateParams.java
@@ -22,6 +22,15 @@ public class SubscriptionItemCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -66,6 +75,7 @@ public class SubscriptionItemCreateParams extends ApiRequestParams {
   private SubscriptionItemCreateParams(
       Object billingThresholds,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String plan,
       Boolean prorate,
@@ -75,6 +85,7 @@ private SubscriptionItemCreateParams(
       Object taxRates) {
     this.billingThresholds = billingThresholds;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.plan = plan;
     this.prorate = prorate;
@@ -93,6 +104,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String plan;
@@ -112,6 +125,7 @@ public SubscriptionItemCreateParams build() {
       return new SubscriptionItemCreateParams(
           this.billingThresholds,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.plan,
           this.prorate,
@@ -165,6 +179,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionItemCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionItemCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -249,11 +289,21 @@ public Builder setTaxRates(List<String> taxRates) {
   }
 
   public static class BillingThresholds {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Usage threshold that triggers the subscription to advance to a new billing period. */
     @SerializedName("usage_gte")
     Long usageGte;
 
-    private BillingThresholds(Long usageGte) {
+    private BillingThresholds(Map<String, Object> extraParams, Long usageGte) {
+      this.extraParams = extraParams;
       this.usageGte = usageGte;
     }
 
@@ -262,11 +312,40 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long usageGte;
 
       /** Finalize and obtain parameter instance from this builder. */
       public BillingThresholds build() {
-        return new BillingThresholds(this.usageGte);
+        return new BillingThresholds(this.extraParams, this.usageGte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionItemCreateParams.BillingThresholds#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionItemCreateParams.BillingThresholds#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Usage threshold that triggers the subscription to advance to a new billing period. */
diff --git a/src/main/java/com/stripe/param/SubscriptionItemDeleteParams.java b/src/main/java/com/stripe/param/SubscriptionItemDeleteParams.java
index f85b6a6109f..f61d49cdb1f 100644
--- a/src/main/java/com/stripe/param/SubscriptionItemDeleteParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionItemDeleteParams.java
@@ -4,6 +4,8 @@
 
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
+import java.util.HashMap;
+import java.util.Map;
 
 public class SubscriptionItemDeleteParams extends ApiRequestParams {
   /**
@@ -13,6 +15,15 @@ public class SubscriptionItemDeleteParams extends ApiRequestParams {
   @SerializedName("clear_usage")
   Boolean clearUsage;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Flag indicating whether to [prorate](https://stripe.com/docs/billing/subscriptions/prorations)
    * switching plans during a billing cycle.
@@ -28,8 +39,10 @@ public class SubscriptionItemDeleteParams extends ApiRequestParams {
   @SerializedName("proration_date")
   Long prorationDate;
 
-  private SubscriptionItemDeleteParams(Boolean clearUsage, Boolean prorate, Long prorationDate) {
+  private SubscriptionItemDeleteParams(
+      Boolean clearUsage, Map<String, Object> extraParams, Boolean prorate, Long prorationDate) {
     this.clearUsage = clearUsage;
+    this.extraParams = extraParams;
     this.prorate = prorate;
     this.prorationDate = prorationDate;
   }
@@ -41,13 +54,16 @@ public static Builder builder() {
   public static class Builder {
     private Boolean clearUsage;
 
+    private Map<String, Object> extraParams;
+
     private Boolean prorate;
 
     private Long prorationDate;
 
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionItemDeleteParams build() {
-      return new SubscriptionItemDeleteParams(this.clearUsage, this.prorate, this.prorationDate);
+      return new SubscriptionItemDeleteParams(
+          this.clearUsage, this.extraParams, this.prorate, this.prorationDate);
     }
 
     /**
@@ -59,6 +75,32 @@ public Builder setClearUsage(Boolean clearUsage) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionItemDeleteParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionItemDeleteParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Flag indicating whether to
      * [prorate](https://stripe.com/docs/billing/subscriptions/prorations) switching plans during a
diff --git a/src/main/java/com/stripe/param/SubscriptionItemListParams.java b/src/main/java/com/stripe/param/SubscriptionItemListParams.java
index 28d13410a0c..c1dbe9e92ff 100644
--- a/src/main/java/com/stripe/param/SubscriptionItemListParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionItemListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionItemListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class SubscriptionItemListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -44,11 +55,13 @@ public class SubscriptionItemListParams extends ApiRequestParams {
   private SubscriptionItemListParams(
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       String subscription) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.subscription = subscription;
@@ -63,6 +76,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -72,7 +87,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionItemListParams build() {
       return new SubscriptionItemListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter, this.subscription);
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter,
+          this.subscription);
     }
 
     /**
@@ -112,6 +132,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionItemListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionItemListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/SubscriptionItemRetrieveParams.java b/src/main/java/com/stripe/param/SubscriptionItemRetrieveParams.java
index f797d53f3c8..002aab82dd2 100644
--- a/src/main/java/com/stripe/param/SubscriptionItemRetrieveParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionItemRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionItemRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private SubscriptionItemRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private SubscriptionItemRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionItemRetrieveParams build() {
-      return new SubscriptionItemRetrieveParams(this.expand);
+      return new SubscriptionItemRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionItemRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionItemRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/SubscriptionItemUpdateParams.java b/src/main/java/com/stripe/param/SubscriptionItemUpdateParams.java
index 3403ad9c977..8c22b29e10c 100644
--- a/src/main/java/com/stripe/param/SubscriptionItemUpdateParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionItemUpdateParams.java
@@ -22,6 +22,15 @@ public class SubscriptionItemUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -62,6 +71,7 @@ public class SubscriptionItemUpdateParams extends ApiRequestParams {
   private SubscriptionItemUpdateParams(
       Object billingThresholds,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String plan,
       Boolean prorate,
@@ -70,6 +80,7 @@ private SubscriptionItemUpdateParams(
       Object taxRates) {
     this.billingThresholds = billingThresholds;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.plan = plan;
     this.prorate = prorate;
@@ -87,6 +98,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String plan;
@@ -104,6 +117,7 @@ public SubscriptionItemUpdateParams build() {
       return new SubscriptionItemUpdateParams(
           this.billingThresholds,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.plan,
           this.prorate,
@@ -156,6 +170,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionItemUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionItemUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -234,11 +274,21 @@ public Builder setTaxRates(List<String> taxRates) {
   }
 
   public static class BillingThresholds {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Usage threshold that triggers the subscription to advance to a new billing period. */
     @SerializedName("usage_gte")
     Long usageGte;
 
-    private BillingThresholds(Long usageGte) {
+    private BillingThresholds(Map<String, Object> extraParams, Long usageGte) {
+      this.extraParams = extraParams;
       this.usageGte = usageGte;
     }
 
@@ -247,11 +297,40 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long usageGte;
 
       /** Finalize and obtain parameter instance from this builder. */
       public BillingThresholds build() {
-        return new BillingThresholds(this.usageGte);
+        return new BillingThresholds(this.extraParams, this.usageGte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionItemUpdateParams.BillingThresholds#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionItemUpdateParams.BillingThresholds#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Usage threshold that triggers the subscription to advance to a new billing period. */
diff --git a/src/main/java/com/stripe/param/SubscriptionItemUsageRecordSummariesParams.java b/src/main/java/com/stripe/param/SubscriptionItemUsageRecordSummariesParams.java
index f019dbf2179..3c5ef027c4f 100644
--- a/src/main/java/com/stripe/param/SubscriptionItemUsageRecordSummariesParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionItemUsageRecordSummariesParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionItemUsageRecordSummariesParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class SubscriptionItemUsageRecordSummariesParams extends ApiRequestParams
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class SubscriptionItemUsageRecordSummariesParams extends ApiRequestParams
   String startingAfter;
 
   private SubscriptionItemUsageRecordSummariesParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionItemUsageRecordSummariesParams build() {
       return new SubscriptionItemUsageRecordSummariesParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,33 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionItemUsageRecordSummariesParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionItemUsageRecordSummariesParams#extraParams} for the field
+     * documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/SubscriptionListParams.java b/src/main/java/com/stripe/param/SubscriptionListParams.java
index 676f8f2d37d..69564a8934f 100644
--- a/src/main/java/com/stripe/param/SubscriptionListParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class SubscriptionListParams extends ApiRequestParams {
@@ -42,6 +44,15 @@ public class SubscriptionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -79,6 +90,7 @@ private SubscriptionListParams(
       String customer,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String plan,
       String startingAfter,
@@ -90,6 +102,7 @@ private SubscriptionListParams(
     this.customer = customer;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.plan = plan;
     this.startingAfter = startingAfter;
@@ -115,6 +128,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String plan;
@@ -133,6 +148,7 @@ public SubscriptionListParams build() {
           this.customer,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.plan,
           this.startingAfter,
@@ -221,6 +237,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -260,6 +302,15 @@ public Builder setStatus(Status status) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -276,7 +327,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -288,6 +340,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -298,7 +352,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -328,6 +408,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class CurrentPeriodEnd {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -344,7 +433,9 @@ public static class CurrentPeriodEnd {
     @SerializedName("lte")
     Long lte;
 
-    private CurrentPeriodEnd(Long gt, Long gte, Long lt, Long lte) {
+    private CurrentPeriodEnd(
+        Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -356,6 +447,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -366,7 +459,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public CurrentPeriodEnd build() {
-        return new CurrentPeriodEnd(this.gt, this.gte, this.lt, this.lte);
+        return new CurrentPeriodEnd(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionListParams.CurrentPeriodEnd#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionListParams.CurrentPeriodEnd#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -396,6 +516,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class CurrentPeriodStart {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -412,7 +541,9 @@ public static class CurrentPeriodStart {
     @SerializedName("lte")
     Long lte;
 
-    private CurrentPeriodStart(Long gt, Long gte, Long lt, Long lte) {
+    private CurrentPeriodStart(
+        Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -424,6 +555,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -434,7 +567,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public CurrentPeriodStart build() {
-        return new CurrentPeriodStart(this.gt, this.gte, this.lt, this.lte);
+        return new CurrentPeriodStart(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionListParams.CurrentPeriodStart#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionListParams.CurrentPeriodStart#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/SubscriptionRetrieveParams.java b/src/main/java/com/stripe/param/SubscriptionRetrieveParams.java
index c3254c55d2b..45096008398 100644
--- a/src/main/java/com/stripe/param/SubscriptionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private SubscriptionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private SubscriptionRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionRetrieveParams build() {
-      return new SubscriptionRetrieveParams(this.expand);
+      return new SubscriptionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleCancelParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleCancelParams.java
index 6ff76036915..bedf3b9fc1e 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleCancelParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleCancelParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionScheduleCancelParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * If the subscription schedule is `active`, indicates whether or not to generate a final invoice
    * that contains any un-invoiced metered usage and new/pending proration invoice items. Defaults
@@ -28,8 +39,9 @@ public class SubscriptionScheduleCancelParams extends ApiRequestParams {
   Boolean prorate;
 
   private SubscriptionScheduleCancelParams(
-      List<String> expand, Boolean invoiceNow, Boolean prorate) {
+      List<String> expand, Map<String, Object> extraParams, Boolean invoiceNow, Boolean prorate) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoiceNow = invoiceNow;
     this.prorate = prorate;
   }
@@ -41,13 +53,16 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean invoiceNow;
 
     private Boolean prorate;
 
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionScheduleCancelParams build() {
-      return new SubscriptionScheduleCancelParams(this.expand, this.invoiceNow, this.prorate);
+      return new SubscriptionScheduleCancelParams(
+          this.expand, this.extraParams, this.invoiceNow, this.prorate);
     }
 
     /**
@@ -76,6 +91,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * If the subscription schedule is `active`, indicates whether or not to generate a final
      * invoice that contains any un-invoiced metered usage and new/pending proration invoice items.
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleCreateParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleCreateParams.java
index 3d94985bb3b..1f2213b0e9d 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleCreateParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleCreateParams.java
@@ -37,6 +37,15 @@ public class SubscriptionScheduleCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Migrate an existing subscription to be managed by a subscription schedule. If this parameter is
    * set, a subscription schedule will be created using the subscription's plan(s), set to
@@ -91,6 +100,7 @@ private SubscriptionScheduleCreateParams(
       Object billingThresholds,
       String customer,
       List<String> expand,
+      Map<String, Object> extraParams,
       String fromSubscription,
       InvoiceSettings invoiceSettings,
       Map<String, String> metadata,
@@ -102,6 +112,7 @@ private SubscriptionScheduleCreateParams(
     this.billingThresholds = billingThresholds;
     this.customer = customer;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.fromSubscription = fromSubscription;
     this.invoiceSettings = invoiceSettings;
     this.metadata = metadata;
@@ -124,6 +135,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String fromSubscription;
 
     private InvoiceSettings invoiceSettings;
@@ -145,6 +158,7 @@ public SubscriptionScheduleCreateParams build() {
           this.billingThresholds,
           this.customer,
           this.expand,
+          this.extraParams,
           this.fromSubscription,
           this.invoiceSettings,
           this.metadata,
@@ -215,6 +229,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Migrate an existing subscription to be managed by a subscription schedule. If this parameter
      * is set, a subscription schedule will be created using the subscription's plan(s), set to
@@ -324,6 +364,15 @@ public static class BillingThresholds {
     @SerializedName("amount_gte")
     Long amountGte;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Indicates if the `billing_cycle_anchor` should be reset when a threshold is reached. If true,
      * `billing_cycle_anchor` will be updated to the date/time the threshold was last reached;
@@ -332,8 +381,10 @@ public static class BillingThresholds {
     @SerializedName("reset_billing_cycle_anchor")
     Boolean resetBillingCycleAnchor;
 
-    private BillingThresholds(Long amountGte, Boolean resetBillingCycleAnchor) {
+    private BillingThresholds(
+        Long amountGte, Map<String, Object> extraParams, Boolean resetBillingCycleAnchor) {
       this.amountGte = amountGte;
+      this.extraParams = extraParams;
       this.resetBillingCycleAnchor = resetBillingCycleAnchor;
     }
 
@@ -344,11 +395,14 @@ public static Builder builder() {
     public static class Builder {
       private Long amountGte;
 
+      private Map<String, Object> extraParams;
+
       private Boolean resetBillingCycleAnchor;
 
       /** Finalize and obtain parameter instance from this builder. */
       public BillingThresholds build() {
-        return new BillingThresholds(this.amountGte, this.resetBillingCycleAnchor);
+        return new BillingThresholds(
+            this.amountGte, this.extraParams, this.resetBillingCycleAnchor);
       }
 
       /** Monetary threshold that triggers the subscription to advance to a new billing period. */
@@ -357,6 +411,34 @@ public Builder setAmountGte(Long amountGte) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleCreateParams.BillingThresholds#extraParams} for the field
+       * documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleCreateParams.BillingThresholds#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Indicates if the `billing_cycle_anchor` should be reset when a threshold is reached. If
        * true, `billing_cycle_anchor` will be updated to the date/time the threshold was last
@@ -373,8 +455,18 @@ public static class InvoiceSettings {
     @SerializedName("days_until_due")
     Long daysUntilDue;
 
-    private InvoiceSettings(Long daysUntilDue) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private InvoiceSettings(Long daysUntilDue, Map<String, Object> extraParams) {
       this.daysUntilDue = daysUntilDue;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -384,15 +476,44 @@ public static Builder builder() {
     public static class Builder {
       private Long daysUntilDue;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public InvoiceSettings build() {
-        return new InvoiceSettings(this.daysUntilDue);
+        return new InvoiceSettings(this.daysUntilDue, this.extraParams);
       }
 
       public Builder setDaysUntilDue(Long daysUntilDue) {
         this.daysUntilDue = daysUntilDue;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleCreateParams.InvoiceSettings#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleCreateParams.InvoiceSettings#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 
@@ -425,6 +546,15 @@ public static class Phase {
     @SerializedName("end_date")
     Long endDate;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Integer representing the multiplier applied to the plan interval. For example, `iterations=2`
      * applied to a plan with `interval=month` and `interval_count=3` results in a phase of duration
@@ -471,6 +601,7 @@ private Phase(
         String coupon,
         Object defaultTaxRates,
         Long endDate,
+        Map<String, Object> extraParams,
         Long iterations,
         List<Plan> plans,
         BigDecimal taxPercent,
@@ -480,6 +611,7 @@ private Phase(
       this.coupon = coupon;
       this.defaultTaxRates = defaultTaxRates;
       this.endDate = endDate;
+      this.extraParams = extraParams;
       this.iterations = iterations;
       this.plans = plans;
       this.taxPercent = taxPercent;
@@ -500,6 +632,8 @@ public static class Builder {
 
       private Long endDate;
 
+      private Map<String, Object> extraParams;
+
       private Long iterations;
 
       private List<Plan> plans;
@@ -517,6 +651,7 @@ public Phase build() {
             this.coupon,
             this.defaultTaxRates,
             this.endDate,
+            this.extraParams,
             this.iterations,
             this.plans,
             this.taxPercent,
@@ -569,6 +704,32 @@ public Builder setEndDate(Long endDate) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleCreateParams.Phase#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleCreateParams.Phase#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Integer representing the multiplier applied to the plan interval. For example,
        * `iterations=2` applied to a plan with `interval=month` and `interval_count=3` results in a
@@ -646,6 +807,15 @@ public static class Plan {
       @SerializedName("billing_thresholds")
       Object billingThresholds;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** The plan ID to subscribe to. */
       @SerializedName("plan")
       String plan;
@@ -664,8 +834,14 @@ public static class Plan {
       @SerializedName("tax_rates")
       Object taxRates;
 
-      private Plan(Object billingThresholds, String plan, Long quantity, Object taxRates) {
+      private Plan(
+          Object billingThresholds,
+          Map<String, Object> extraParams,
+          String plan,
+          Long quantity,
+          Object taxRates) {
         this.billingThresholds = billingThresholds;
+        this.extraParams = extraParams;
         this.plan = plan;
         this.quantity = quantity;
         this.taxRates = taxRates;
@@ -678,6 +854,8 @@ public static Builder builder() {
       public static class Builder {
         private Object billingThresholds;
 
+        private Map<String, Object> extraParams;
+
         private String plan;
 
         private Long quantity;
@@ -686,7 +864,8 @@ public static class Builder {
 
         /** Finalize and obtain parameter instance from this builder. */
         public Plan build() {
-          return new Plan(this.billingThresholds, this.plan, this.quantity, this.taxRates);
+          return new Plan(
+              this.billingThresholds, this.extraParams, this.plan, this.quantity, this.taxRates);
         }
 
         /**
@@ -707,6 +886,34 @@ public Builder setBillingThresholds(EmptyParam billingThresholds) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SubscriptionScheduleCreateParams.Phase.Plan#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SubscriptionScheduleCreateParams.Phase.Plan#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** The plan ID to subscribe to. */
         public Builder setPlan(String plan) {
           this.plan = plan;
@@ -742,11 +949,22 @@ public Builder setTaxRates(List<String> taxRates) {
       }
 
       public static class BillingThresholds {
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
         /** Usage threshold that triggers the subscription to advance to a new billing period. */
         @SerializedName("usage_gte")
         Long usageGte;
 
-        private BillingThresholds(Long usageGte) {
+        private BillingThresholds(Map<String, Object> extraParams, Long usageGte) {
+          this.extraParams = extraParams;
           this.usageGte = usageGte;
         }
 
@@ -756,11 +974,43 @@ public static Builder builder() {
         }
 
         public static class Builder {
+          private Map<String, Object> extraParams;
+
           private Long usageGte;
 
           /** Finalize and obtain parameter instance from this builder. */
           public BillingThresholds build() {
-            return new BillingThresholds(this.usageGte);
+            return new BillingThresholds(this.extraParams, this.usageGte);
+          }
+
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link
+           * SubscriptionScheduleCreateParams.Phase.Plan.BillingThresholds#extraParams} for the
+           * field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link
+           * SubscriptionScheduleCreateParams.Phase.Plan.BillingThresholds#extraParams} for the
+           * field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
           }
 
           /** Usage threshold that triggers the subscription to advance to a new billing period. */
@@ -774,6 +1024,15 @@ public Builder setUsageGte(Long usageGte) {
   }
 
   public static class RenewalInterval {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Interval at which to renew the subscription schedule for when it ends. Possible values are
      * `day`, `week`, `month`, or `year`.
@@ -785,7 +1044,8 @@ public static class RenewalInterval {
     @SerializedName("length")
     Long length;
 
-    private RenewalInterval(Interval interval, Long length) {
+    private RenewalInterval(Map<String, Object> extraParams, Interval interval, Long length) {
+      this.extraParams = extraParams;
       this.interval = interval;
       this.length = length;
     }
@@ -795,13 +1055,42 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Interval interval;
 
       private Long length;
 
       /** Finalize and obtain parameter instance from this builder. */
       public RenewalInterval build() {
-        return new RenewalInterval(this.interval, this.length);
+        return new RenewalInterval(this.extraParams, this.interval, this.length);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleCreateParams.RenewalInterval#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleCreateParams.RenewalInterval#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /**
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleListParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleListParams.java
index 65da7c19126..f051ca928c9 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleListParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionScheduleListParams extends ApiRequestParams {
   /** Only return subscription schedules that were created canceled the given date interval. */
@@ -37,6 +39,15 @@ public class SubscriptionScheduleListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -68,6 +79,7 @@ private SubscriptionScheduleListParams(
       String customer,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       Object releasedAt,
       Boolean scheduled,
@@ -78,6 +90,7 @@ private SubscriptionScheduleListParams(
     this.customer = customer;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.releasedAt = releasedAt;
     this.scheduled = scheduled;
@@ -101,6 +114,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private Object releasedAt;
@@ -118,6 +133,7 @@ public SubscriptionScheduleListParams build() {
           this.customer,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.releasedAt,
           this.scheduled,
@@ -203,6 +219,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -243,6 +285,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class CanceledAt {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -259,7 +310,8 @@ public static class CanceledAt {
     @SerializedName("lte")
     Long lte;
 
-    private CanceledAt(Long gt, Long gte, Long lt, Long lte) {
+    private CanceledAt(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -271,6 +323,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -281,7 +335,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public CanceledAt build() {
-        return new CanceledAt(this.gt, this.gte, this.lt, this.lte);
+        return new CanceledAt(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleListParams.CanceledAt#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleListParams.CanceledAt#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -311,6 +392,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class CompletedAt {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -327,7 +417,8 @@ public static class CompletedAt {
     @SerializedName("lte")
     Long lte;
 
-    private CompletedAt(Long gt, Long gte, Long lt, Long lte) {
+    private CompletedAt(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -339,6 +430,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -349,7 +442,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public CompletedAt build() {
-        return new CompletedAt(this.gt, this.gte, this.lt, this.lte);
+        return new CompletedAt(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleListParams.CompletedAt#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleListParams.CompletedAt#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -379,6 +499,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -395,7 +524,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -407,6 +537,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -417,7 +549,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -447,6 +605,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class ReleasedAt {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -463,7 +630,8 @@ public static class ReleasedAt {
     @SerializedName("lte")
     Long lte;
 
-    private ReleasedAt(Long gt, Long gte, Long lt, Long lte) {
+    private ReleasedAt(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -475,6 +643,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -485,7 +655,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public ReleasedAt build() {
-        return new ReleasedAt(this.gt, this.gte, this.lt, this.lte);
+        return new ReleasedAt(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleListParams.ReleasedAt#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleListParams.ReleasedAt#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleReleaseParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleReleaseParams.java
index 1d12f38ca7f..76344c2d138 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleReleaseParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleReleaseParams.java
@@ -5,19 +5,32 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionScheduleReleaseParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Keep any cancellation on the subscription that the schedule has set. */
   @SerializedName("preserve_cancel_date")
   Boolean preserveCancelDate;
 
-  private SubscriptionScheduleReleaseParams(List<String> expand, Boolean preserveCancelDate) {
+  private SubscriptionScheduleReleaseParams(
+      List<String> expand, Map<String, Object> extraParams, Boolean preserveCancelDate) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.preserveCancelDate = preserveCancelDate;
   }
 
@@ -28,11 +41,14 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean preserveCancelDate;
 
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionScheduleReleaseParams build() {
-      return new SubscriptionScheduleReleaseParams(this.expand, this.preserveCancelDate);
+      return new SubscriptionScheduleReleaseParams(
+          this.expand, this.extraParams, this.preserveCancelDate);
     }
 
     /**
@@ -61,6 +77,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleReleaseParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleReleaseParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Keep any cancellation on the subscription that the schedule has set. */
     public Builder setPreserveCancelDate(Boolean preserveCancelDate) {
       this.preserveCancelDate = preserveCancelDate;
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleRetrieveParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleRetrieveParams.java
index 056a5bb048a..8489a813d31 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleRetrieveParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionScheduleRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private SubscriptionScheduleRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private SubscriptionScheduleRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionScheduleRetrieveParams build() {
-      return new SubscriptionScheduleRetrieveParams(this.expand);
+      return new SubscriptionScheduleRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleRevisionCollectionListParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleRevisionCollectionListParams.java
index 2644a7ebc32..c218aab10dc 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleRevisionCollectionListParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleRevisionCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionScheduleRevisionCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class SubscriptionScheduleRevisionCollectionListParams extends ApiRequest
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class SubscriptionScheduleRevisionCollectionListParams extends ApiRequest
   String startingAfter;
 
   private SubscriptionScheduleRevisionCollectionListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionScheduleRevisionCollectionListParams build() {
       return new SubscriptionScheduleRevisionCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,33 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleRevisionCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleRevisionCollectionListParams#extraParams} for the field
+     * documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleRevisionCollectionRetrieveParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleRevisionCollectionRetrieveParams.java
index 53305c56959..7b928e40839 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleRevisionCollectionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleRevisionCollectionRetrieveParams.java
@@ -5,15 +5,28 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionScheduleRevisionCollectionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private SubscriptionScheduleRevisionCollectionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private SubscriptionScheduleRevisionCollectionRetrieveParams(
+      List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +36,12 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionScheduleRevisionCollectionRetrieveParams build() {
-      return new SubscriptionScheduleRevisionCollectionRetrieveParams(this.expand);
+      return new SubscriptionScheduleRevisionCollectionRetrieveParams(
+          this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +69,33 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleRevisionCollectionRetrieveParams#extraParams} for the field
+     * documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleRevisionCollectionRetrieveParams#extraParams} for the field
+     * documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleRevisionsParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleRevisionsParams.java
index 05f43613166..cf789556f7d 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleRevisionsParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleRevisionsParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SubscriptionScheduleRevisionsParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class SubscriptionScheduleRevisionsParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class SubscriptionScheduleRevisionsParams extends ApiRequestParams {
   String startingAfter;
 
   private SubscriptionScheduleRevisionsParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public SubscriptionScheduleRevisionsParams build() {
       return new SubscriptionScheduleRevisionsParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleRevisionsParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleRevisionsParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/SubscriptionScheduleUpdateParams.java b/src/main/java/com/stripe/param/SubscriptionScheduleUpdateParams.java
index 89467a0d162..14b21b8be68 100644
--- a/src/main/java/com/stripe/param/SubscriptionScheduleUpdateParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionScheduleUpdateParams.java
@@ -33,6 +33,15 @@ public class SubscriptionScheduleUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** All invoices will be billed using the specified settings. */
   @SerializedName("invoice_settings")
   InvoiceSettings invoiceSettings;
@@ -81,6 +90,7 @@ private SubscriptionScheduleUpdateParams(
       Billing billing,
       Object billingThresholds,
       List<String> expand,
+      Map<String, Object> extraParams,
       InvoiceSettings invoiceSettings,
       Map<String, String> metadata,
       List<Phase> phases,
@@ -90,6 +100,7 @@ private SubscriptionScheduleUpdateParams(
     this.billing = billing;
     this.billingThresholds = billingThresholds;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.invoiceSettings = invoiceSettings;
     this.metadata = metadata;
     this.phases = phases;
@@ -109,6 +120,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private InvoiceSettings invoiceSettings;
 
     private Map<String, String> metadata;
@@ -127,6 +140,7 @@ public SubscriptionScheduleUpdateParams build() {
           this.billing,
           this.billingThresholds,
           this.expand,
+          this.extraParams,
           this.invoiceSettings,
           this.metadata,
           this.phases,
@@ -190,6 +204,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionScheduleUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionScheduleUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** All invoices will be billed using the specified settings. */
     public Builder setInvoiceSettings(InvoiceSettings invoiceSettings) {
       this.invoiceSettings = invoiceSettings;
@@ -285,6 +325,15 @@ public static class BillingThresholds {
     @SerializedName("amount_gte")
     Long amountGte;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Indicates if the `billing_cycle_anchor` should be reset when a threshold is reached. If true,
      * `billing_cycle_anchor` will be updated to the date/time the threshold was last reached;
@@ -293,8 +342,10 @@ public static class BillingThresholds {
     @SerializedName("reset_billing_cycle_anchor")
     Boolean resetBillingCycleAnchor;
 
-    private BillingThresholds(Long amountGte, Boolean resetBillingCycleAnchor) {
+    private BillingThresholds(
+        Long amountGte, Map<String, Object> extraParams, Boolean resetBillingCycleAnchor) {
       this.amountGte = amountGte;
+      this.extraParams = extraParams;
       this.resetBillingCycleAnchor = resetBillingCycleAnchor;
     }
 
@@ -305,11 +356,14 @@ public static Builder builder() {
     public static class Builder {
       private Long amountGte;
 
+      private Map<String, Object> extraParams;
+
       private Boolean resetBillingCycleAnchor;
 
       /** Finalize and obtain parameter instance from this builder. */
       public BillingThresholds build() {
-        return new BillingThresholds(this.amountGte, this.resetBillingCycleAnchor);
+        return new BillingThresholds(
+            this.amountGte, this.extraParams, this.resetBillingCycleAnchor);
       }
 
       /** Monetary threshold that triggers the subscription to advance to a new billing period. */
@@ -318,6 +372,34 @@ public Builder setAmountGte(Long amountGte) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleUpdateParams.BillingThresholds#extraParams} for the field
+       * documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleUpdateParams.BillingThresholds#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Indicates if the `billing_cycle_anchor` should be reset when a threshold is reached. If
        * true, `billing_cycle_anchor` will be updated to the date/time the threshold was last
@@ -334,8 +416,18 @@ public static class InvoiceSettings {
     @SerializedName("days_until_due")
     Long daysUntilDue;
 
-    private InvoiceSettings(Long daysUntilDue) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private InvoiceSettings(Long daysUntilDue, Map<String, Object> extraParams) {
       this.daysUntilDue = daysUntilDue;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -345,15 +437,44 @@ public static Builder builder() {
     public static class Builder {
       private Long daysUntilDue;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public InvoiceSettings build() {
-        return new InvoiceSettings(this.daysUntilDue);
+        return new InvoiceSettings(this.daysUntilDue, this.extraParams);
       }
 
       public Builder setDaysUntilDue(Long daysUntilDue) {
         this.daysUntilDue = daysUntilDue;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleUpdateParams.InvoiceSettings#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleUpdateParams.InvoiceSettings#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 
@@ -386,6 +507,15 @@ public static class Phase {
     @SerializedName("end_date")
     Object endDate;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Integer representing the multiplier applied to the plan interval. For example, `iterations=2`
      * applied to a plan with `interval=month` and `interval_count=3` results in a phase of duration
@@ -436,6 +566,7 @@ private Phase(
         String coupon,
         Object defaultTaxRates,
         Object endDate,
+        Map<String, Object> extraParams,
         Long iterations,
         List<Plan> plans,
         Object startDate,
@@ -446,6 +577,7 @@ private Phase(
       this.coupon = coupon;
       this.defaultTaxRates = defaultTaxRates;
       this.endDate = endDate;
+      this.extraParams = extraParams;
       this.iterations = iterations;
       this.plans = plans;
       this.startDate = startDate;
@@ -467,6 +599,8 @@ public static class Builder {
 
       private Object endDate;
 
+      private Map<String, Object> extraParams;
+
       private Long iterations;
 
       private List<Plan> plans;
@@ -486,6 +620,7 @@ public Phase build() {
             this.coupon,
             this.defaultTaxRates,
             this.endDate,
+            this.extraParams,
             this.iterations,
             this.plans,
             this.startDate,
@@ -548,6 +683,32 @@ public Builder setEndDate(Long endDate) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleUpdateParams.Phase#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleUpdateParams.Phase#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Integer representing the multiplier applied to the plan interval. For example,
        * `iterations=2` applied to a plan with `interval=month` and `interval_count=3` results in a
@@ -646,6 +807,15 @@ public static class Plan {
       @SerializedName("billing_thresholds")
       Object billingThresholds;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** The plan ID to subscribe to. */
       @SerializedName("plan")
       String plan;
@@ -664,8 +834,14 @@ public static class Plan {
       @SerializedName("tax_rates")
       Object taxRates;
 
-      private Plan(Object billingThresholds, String plan, Long quantity, Object taxRates) {
+      private Plan(
+          Object billingThresholds,
+          Map<String, Object> extraParams,
+          String plan,
+          Long quantity,
+          Object taxRates) {
         this.billingThresholds = billingThresholds;
+        this.extraParams = extraParams;
         this.plan = plan;
         this.quantity = quantity;
         this.taxRates = taxRates;
@@ -678,6 +854,8 @@ public static Builder builder() {
       public static class Builder {
         private Object billingThresholds;
 
+        private Map<String, Object> extraParams;
+
         private String plan;
 
         private Long quantity;
@@ -686,7 +864,8 @@ public static class Builder {
 
         /** Finalize and obtain parameter instance from this builder. */
         public Plan build() {
-          return new Plan(this.billingThresholds, this.plan, this.quantity, this.taxRates);
+          return new Plan(
+              this.billingThresholds, this.extraParams, this.plan, this.quantity, this.taxRates);
         }
 
         /**
@@ -707,6 +886,34 @@ public Builder setBillingThresholds(EmptyParam billingThresholds) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SubscriptionScheduleUpdateParams.Phase.Plan#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SubscriptionScheduleUpdateParams.Phase.Plan#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** The plan ID to subscribe to. */
         public Builder setPlan(String plan) {
           this.plan = plan;
@@ -742,11 +949,22 @@ public Builder setTaxRates(List<String> taxRates) {
       }
 
       public static class BillingThresholds {
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
         /** Usage threshold that triggers the subscription to advance to a new billing period. */
         @SerializedName("usage_gte")
         Long usageGte;
 
-        private BillingThresholds(Long usageGte) {
+        private BillingThresholds(Map<String, Object> extraParams, Long usageGte) {
+          this.extraParams = extraParams;
           this.usageGte = usageGte;
         }
 
@@ -756,11 +974,43 @@ public static Builder builder() {
         }
 
         public static class Builder {
+          private Map<String, Object> extraParams;
+
           private Long usageGte;
 
           /** Finalize and obtain parameter instance from this builder. */
           public BillingThresholds build() {
-            return new BillingThresholds(this.usageGte);
+            return new BillingThresholds(this.extraParams, this.usageGte);
+          }
+
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link
+           * SubscriptionScheduleUpdateParams.Phase.Plan.BillingThresholds#extraParams} for the
+           * field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link
+           * SubscriptionScheduleUpdateParams.Phase.Plan.BillingThresholds#extraParams} for the
+           * field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
           }
 
           /** Usage threshold that triggers the subscription to advance to a new billing period. */
@@ -810,6 +1060,15 @@ public enum TrialEnd implements ApiRequestParams.EnumParam {
   }
 
   public static class RenewalInterval {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Interval at which to renew the subscription schedule for when it ends. Possible values are
      * `day`, `week`, `month`, or `year`.
@@ -821,7 +1080,8 @@ public static class RenewalInterval {
     @SerializedName("length")
     Long length;
 
-    private RenewalInterval(Interval interval, Long length) {
+    private RenewalInterval(Map<String, Object> extraParams, Interval interval, Long length) {
+      this.extraParams = extraParams;
       this.interval = interval;
       this.length = length;
     }
@@ -831,13 +1091,42 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Interval interval;
 
       private Long length;
 
       /** Finalize and obtain parameter instance from this builder. */
       public RenewalInterval build() {
-        return new RenewalInterval(this.interval, this.length);
+        return new RenewalInterval(this.extraParams, this.interval, this.length);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionScheduleUpdateParams.RenewalInterval#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionScheduleUpdateParams.RenewalInterval#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /**
diff --git a/src/main/java/com/stripe/param/SubscriptionUpdateParams.java b/src/main/java/com/stripe/param/SubscriptionUpdateParams.java
index 9ca785bef9c..c8026555e20 100644
--- a/src/main/java/com/stripe/param/SubscriptionUpdateParams.java
+++ b/src/main/java/com/stripe/param/SubscriptionUpdateParams.java
@@ -101,6 +101,15 @@ public class SubscriptionUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** List of subscription items, each with an attached plan. */
   @SerializedName("items")
   List<Item> items;
@@ -183,6 +192,7 @@ private SubscriptionUpdateParams(
       String defaultSource,
       Object defaultTaxRates,
       List<String> expand,
+      Map<String, Object> extraParams,
       List<Item> items,
       Map<String, String> metadata,
       Boolean prorate,
@@ -203,6 +213,7 @@ private SubscriptionUpdateParams(
     this.defaultSource = defaultSource;
     this.defaultTaxRates = defaultTaxRates;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.items = items;
     this.metadata = metadata;
     this.prorate = prorate;
@@ -242,6 +253,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<Item> items;
 
     private Map<String, String> metadata;
@@ -273,6 +286,7 @@ public SubscriptionUpdateParams build() {
           this.defaultSource,
           this.defaultTaxRates,
           this.expand,
+          this.extraParams,
           this.items,
           this.metadata,
           this.prorate,
@@ -442,6 +456,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SubscriptionUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SubscriptionUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `items` list. A list is initialized for the first `add/addAll` call, and
      * subsequent calls adds additional elements to the original list. See {@link
@@ -606,6 +646,15 @@ public static class BillingThresholds {
     @SerializedName("amount_gte")
     Long amountGte;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Indicates if the `billing_cycle_anchor` should be reset when a threshold is reached. If true,
      * `billing_cycle_anchor` will be updated to the date/time the threshold was last reached;
@@ -614,8 +663,10 @@ public static class BillingThresholds {
     @SerializedName("reset_billing_cycle_anchor")
     Boolean resetBillingCycleAnchor;
 
-    private BillingThresholds(Long amountGte, Boolean resetBillingCycleAnchor) {
+    private BillingThresholds(
+        Long amountGte, Map<String, Object> extraParams, Boolean resetBillingCycleAnchor) {
       this.amountGte = amountGte;
+      this.extraParams = extraParams;
       this.resetBillingCycleAnchor = resetBillingCycleAnchor;
     }
 
@@ -626,11 +677,14 @@ public static Builder builder() {
     public static class Builder {
       private Long amountGte;
 
+      private Map<String, Object> extraParams;
+
       private Boolean resetBillingCycleAnchor;
 
       /** Finalize and obtain parameter instance from this builder. */
       public BillingThresholds build() {
-        return new BillingThresholds(this.amountGte, this.resetBillingCycleAnchor);
+        return new BillingThresholds(
+            this.amountGte, this.extraParams, this.resetBillingCycleAnchor);
       }
 
       /** Monetary threshold that triggers the subscription to advance to a new billing period. */
@@ -639,6 +693,33 @@ public Builder setAmountGte(Long amountGte) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionUpdateParams.BillingThresholds#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionUpdateParams.BillingThresholds#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Indicates if the `billing_cycle_anchor` should be reset when a threshold is reached. If
        * true, `billing_cycle_anchor` will be updated to the date/time the threshold was last
@@ -670,6 +751,15 @@ public static class Item {
     @SerializedName("deleted")
     Boolean deleted;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Subscription item to update. */
     @SerializedName("id")
     String id;
@@ -700,6 +790,7 @@ private Item(
         Object billingThresholds,
         Boolean clearUsage,
         Boolean deleted,
+        Map<String, Object> extraParams,
         String id,
         Map<String, String> metadata,
         String plan,
@@ -708,6 +799,7 @@ private Item(
       this.billingThresholds = billingThresholds;
       this.clearUsage = clearUsage;
       this.deleted = deleted;
+      this.extraParams = extraParams;
       this.id = id;
       this.metadata = metadata;
       this.plan = plan;
@@ -726,6 +818,8 @@ public static class Builder {
 
       private Boolean deleted;
 
+      private Map<String, Object> extraParams;
+
       private String id;
 
       private Map<String, String> metadata;
@@ -742,6 +836,7 @@ public Item build() {
             this.billingThresholds,
             this.clearUsage,
             this.deleted,
+            this.extraParams,
             this.id,
             this.metadata,
             this.plan,
@@ -782,6 +877,32 @@ public Builder setDeleted(Boolean deleted) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionUpdateParams.Item#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionUpdateParams.Item#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Subscription item to update. */
       public Builder setId(String id) {
         this.id = id;
@@ -846,11 +967,21 @@ public Builder setTaxRates(List<String> taxRates) {
     }
 
     public static class BillingThresholds {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Usage threshold that triggers the subscription to advance to a new billing period. */
       @SerializedName("usage_gte")
       Long usageGte;
 
-      private BillingThresholds(Long usageGte) {
+      private BillingThresholds(Map<String, Object> extraParams, Long usageGte) {
+        this.extraParams = extraParams;
         this.usageGte = usageGte;
       }
 
@@ -859,11 +990,41 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private Long usageGte;
 
         /** Finalize and obtain parameter instance from this builder. */
         public BillingThresholds build() {
-          return new BillingThresholds(this.usageGte);
+          return new BillingThresholds(this.extraParams, this.usageGte);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SubscriptionUpdateParams.Item.BillingThresholds#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SubscriptionUpdateParams.Item.BillingThresholds#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** Usage threshold that triggers the subscription to advance to a new billing period. */
@@ -880,8 +1041,18 @@ public static class TransferData {
     @SerializedName("destination")
     String destination;
 
-    private TransferData(String destination) {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
+    private TransferData(String destination, Map<String, Object> extraParams) {
       this.destination = destination;
+      this.extraParams = extraParams;
     }
 
     public static Builder builder() {
@@ -891,9 +1062,11 @@ public static Builder builder() {
     public static class Builder {
       private String destination;
 
+      private Map<String, Object> extraParams;
+
       /** Finalize and obtain parameter instance from this builder. */
       public TransferData build() {
-        return new TransferData(this.destination);
+        return new TransferData(this.destination, this.extraParams);
       }
 
       /** ID of an existing, connected Stripe account. */
@@ -901,6 +1074,32 @@ public Builder setDestination(String destination) {
         this.destination = destination;
         return this;
       }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SubscriptionUpdateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SubscriptionUpdateParams.TransferData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
     }
   }
 
diff --git a/src/main/java/com/stripe/param/TaxIdCollectionCreateParams.java b/src/main/java/com/stripe/param/TaxIdCollectionCreateParams.java
index 330cb6e54bf..2836e5dd25f 100644
--- a/src/main/java/com/stripe/param/TaxIdCollectionCreateParams.java
+++ b/src/main/java/com/stripe/param/TaxIdCollectionCreateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class TaxIdCollectionCreateParams extends ApiRequestParams {
@@ -13,6 +15,15 @@ public class TaxIdCollectionCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Type of the tax ID, one of `eu_vat`, `nz_gst`, or `au_abn`. */
   @SerializedName("type")
   Type type;
@@ -21,8 +32,10 @@ public class TaxIdCollectionCreateParams extends ApiRequestParams {
   @SerializedName("value")
   String value;
 
-  private TaxIdCollectionCreateParams(List<String> expand, Type type, String value) {
+  private TaxIdCollectionCreateParams(
+      List<String> expand, Map<String, Object> extraParams, Type type, String value) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.type = type;
     this.value = value;
   }
@@ -34,13 +47,15 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Type type;
 
     private String value;
 
     /** Finalize and obtain parameter instance from this builder. */
     public TaxIdCollectionCreateParams build() {
-      return new TaxIdCollectionCreateParams(this.expand, this.type, this.value);
+      return new TaxIdCollectionCreateParams(this.expand, this.extraParams, this.type, this.value);
     }
 
     /**
@@ -69,6 +84,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TaxIdCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TaxIdCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Type of the tax ID, one of `eu_vat`, `nz_gst`, or `au_abn`. */
     public Builder setType(Type type) {
       this.type = type;
diff --git a/src/main/java/com/stripe/param/TaxIdCollectionListParams.java b/src/main/java/com/stripe/param/TaxIdCollectionListParams.java
index fbec1cedee0..7e3727e3373 100644
--- a/src/main/java/com/stripe/param/TaxIdCollectionListParams.java
+++ b/src/main/java/com/stripe/param/TaxIdCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TaxIdCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class TaxIdCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class TaxIdCollectionListParams extends ApiRequestParams {
   String startingAfter;
 
   private TaxIdCollectionListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public TaxIdCollectionListParams build() {
       return new TaxIdCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TaxIdCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TaxIdCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/TaxIdCollectionRetrieveParams.java b/src/main/java/com/stripe/param/TaxIdCollectionRetrieveParams.java
index b48d96098d2..274ec1c1754 100644
--- a/src/main/java/com/stripe/param/TaxIdCollectionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/TaxIdCollectionRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TaxIdCollectionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private TaxIdCollectionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private TaxIdCollectionRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public TaxIdCollectionRetrieveParams build() {
-      return new TaxIdCollectionRetrieveParams(this.expand);
+      return new TaxIdCollectionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TaxIdCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TaxIdCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/TaxRateCreateParams.java b/src/main/java/com/stripe/param/TaxRateCreateParams.java
index 46e97815c2a..7c3c64b6ec9 100644
--- a/src/main/java/com/stripe/param/TaxRateCreateParams.java
+++ b/src/main/java/com/stripe/param/TaxRateCreateParams.java
@@ -33,6 +33,15 @@ public class TaxRateCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** This specifies if the tax rate is inclusive or exclusive. */
   @SerializedName("inclusive")
   Boolean inclusive;
@@ -58,6 +67,7 @@ private TaxRateCreateParams(
       String description,
       String displayName,
       List<String> expand,
+      Map<String, Object> extraParams,
       Boolean inclusive,
       String jurisdiction,
       Map<String, String> metadata,
@@ -66,6 +76,7 @@ private TaxRateCreateParams(
     this.description = description;
     this.displayName = displayName;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.inclusive = inclusive;
     this.jurisdiction = jurisdiction;
     this.metadata = metadata;
@@ -85,6 +96,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean inclusive;
 
     private String jurisdiction;
@@ -100,6 +113,7 @@ public TaxRateCreateParams build() {
           this.description,
           this.displayName,
           this.expand,
+          this.extraParams,
           this.inclusive,
           this.jurisdiction,
           this.metadata,
@@ -156,6 +170,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TaxRateCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TaxRateCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** This specifies if the tax rate is inclusive or exclusive. */
     public Builder setInclusive(Boolean inclusive) {
       this.inclusive = inclusive;
diff --git a/src/main/java/com/stripe/param/TaxRateListParams.java b/src/main/java/com/stripe/param/TaxRateListParams.java
index 420c1ec3683..a49ab104089 100644
--- a/src/main/java/com/stripe/param/TaxRateListParams.java
+++ b/src/main/java/com/stripe/param/TaxRateListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TaxRateListParams extends ApiRequestParams {
   /** Optional flag to filter by tax rates that are either active or not active (archived). */
@@ -29,6 +31,15 @@ public class TaxRateListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Optional flag to filter by tax rates that are inclusive (or those that are not inclusive). */
   @SerializedName("inclusive")
   Boolean inclusive;
@@ -58,6 +69,7 @@ private TaxRateListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Boolean inclusive,
       Long limit,
       Object percentage,
@@ -66,6 +78,7 @@ private TaxRateListParams(
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.inclusive = inclusive;
     this.limit = limit;
     this.percentage = percentage;
@@ -85,6 +98,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean inclusive;
 
     private Long limit;
@@ -100,6 +115,7 @@ public TaxRateListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.inclusive,
           this.limit,
           this.percentage,
@@ -161,6 +177,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TaxRateListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TaxRateListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Optional flag to filter by tax rates that are inclusive (or those that are not inclusive).
      */
@@ -203,6 +245,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -219,7 +270,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -231,6 +283,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -241,7 +295,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TaxRateListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TaxRateListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -271,6 +351,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class Percentage {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -287,7 +376,8 @@ public static class Percentage {
     @SerializedName("lte")
     Long lte;
 
-    private Percentage(Long gt, Long gte, Long lt, Long lte) {
+    private Percentage(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -299,6 +389,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -309,7 +401,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Percentage build() {
-        return new Percentage(this.gt, this.gte, this.lt, this.lte);
+        return new Percentage(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TaxRateListParams.Percentage#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TaxRateListParams.Percentage#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/TaxRateRetrieveParams.java b/src/main/java/com/stripe/param/TaxRateRetrieveParams.java
index af69b9448c9..ef90dc2fc29 100644
--- a/src/main/java/com/stripe/param/TaxRateRetrieveParams.java
+++ b/src/main/java/com/stripe/param/TaxRateRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TaxRateRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private TaxRateRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private TaxRateRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public TaxRateRetrieveParams build() {
-      return new TaxRateRetrieveParams(this.expand);
+      return new TaxRateRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TaxRateRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TaxRateRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/TaxRateUpdateParams.java b/src/main/java/com/stripe/param/TaxRateUpdateParams.java
index a218333f74d..b716ca28a39 100644
--- a/src/main/java/com/stripe/param/TaxRateUpdateParams.java
+++ b/src/main/java/com/stripe/param/TaxRateUpdateParams.java
@@ -32,6 +32,15 @@ public class TaxRateUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The jurisdiction for the tax rate. */
   @SerializedName("jurisdiction")
   String jurisdiction;
@@ -49,12 +58,14 @@ private TaxRateUpdateParams(
       String description,
       String displayName,
       List<String> expand,
+      Map<String, Object> extraParams,
       String jurisdiction,
       Map<String, String> metadata) {
     this.active = active;
     this.description = description;
     this.displayName = displayName;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.jurisdiction = jurisdiction;
     this.metadata = metadata;
   }
@@ -72,6 +83,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String jurisdiction;
 
     private Map<String, String> metadata;
@@ -83,6 +96,7 @@ public TaxRateUpdateParams build() {
           this.description,
           this.displayName,
           this.expand,
+          this.extraParams,
           this.jurisdiction,
           this.metadata);
     }
@@ -137,6 +151,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TaxRateUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TaxRateUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The jurisdiction for the tax rate. */
     public Builder setJurisdiction(String jurisdiction) {
       this.jurisdiction = jurisdiction;
diff --git a/src/main/java/com/stripe/param/ThreeDSecureCreateParams.java b/src/main/java/com/stripe/param/ThreeDSecureCreateParams.java
index c29163c491d..cb67404556c 100644
--- a/src/main/java/com/stripe/param/ThreeDSecureCreateParams.java
+++ b/src/main/java/com/stripe/param/ThreeDSecureCreateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ThreeDSecureCreateParams extends ApiRequestParams {
   /** Amount of the charge that you will create when authentication completes. */
@@ -30,6 +32,15 @@ public class ThreeDSecureCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The URL that the cardholder's browser will be returned to when authentication completes. */
   @SerializedName("return_url")
   String returnUrl;
@@ -40,12 +51,14 @@ private ThreeDSecureCreateParams(
       String currency,
       String customer,
       List<String> expand,
+      Map<String, Object> extraParams,
       String returnUrl) {
     this.amount = amount;
     this.card = card;
     this.currency = currency;
     this.customer = customer;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.returnUrl = returnUrl;
   }
 
@@ -64,12 +77,20 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String returnUrl;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ThreeDSecureCreateParams build() {
       return new ThreeDSecureCreateParams(
-          this.amount, this.card, this.currency, this.customer, this.expand, this.returnUrl);
+          this.amount,
+          this.card,
+          this.currency,
+          this.customer,
+          this.expand,
+          this.extraParams,
+          this.returnUrl);
     }
 
     /** Amount of the charge that you will create when authentication completes. */
@@ -124,6 +145,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ThreeDSecureCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ThreeDSecureCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The URL that the cardholder's browser will be returned to when authentication completes. */
     public Builder setReturnUrl(String returnUrl) {
       this.returnUrl = returnUrl;
diff --git a/src/main/java/com/stripe/param/ThreeDSecureRetrieveParams.java b/src/main/java/com/stripe/param/ThreeDSecureRetrieveParams.java
index 56f9b3f6e35..1e7ac144a19 100644
--- a/src/main/java/com/stripe/param/ThreeDSecureRetrieveParams.java
+++ b/src/main/java/com/stripe/param/ThreeDSecureRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ThreeDSecureRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ThreeDSecureRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ThreeDSecureRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ThreeDSecureRetrieveParams build() {
-      return new ThreeDSecureRetrieveParams(this.expand);
+      return new ThreeDSecureRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ThreeDSecureRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ThreeDSecureRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/TokenCreateParams.java b/src/main/java/com/stripe/param/TokenCreateParams.java
index 5727d31839a..ae661668664 100644
--- a/src/main/java/com/stripe/param/TokenCreateParams.java
+++ b/src/main/java/com/stripe/param/TokenCreateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class TokenCreateParams extends ApiRequestParams {
@@ -30,16 +32,31 @@ public class TokenCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The PII this token will represent. */
   @SerializedName("pii")
   Pii pii;
 
   private TokenCreateParams(
-      BankAccount bankAccount, Object card, String customer, List<String> expand, Pii pii) {
+      BankAccount bankAccount,
+      Object card,
+      String customer,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Pii pii) {
     this.bankAccount = bankAccount;
     this.card = card;
     this.customer = customer;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.pii = pii;
   }
 
@@ -56,12 +73,14 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Pii pii;
 
     /** Finalize and obtain parameter instance from this builder. */
     public TokenCreateParams build() {
       return new TokenCreateParams(
-          this.bankAccount, this.card, this.customer, this.expand, this.pii);
+          this.bankAccount, this.card, this.customer, this.expand, this.extraParams, this.pii);
     }
 
     /** The bank account this token will represent. */
@@ -118,6 +137,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TokenCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TokenCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The PII this token will represent. */
     public Builder setPii(Pii pii) {
       this.pii = pii;
@@ -155,6 +200,15 @@ public static class BankAccount {
     @SerializedName("currency")
     String currency;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * The routing number, sort code, or other country-appropriateinstitution number for the bank
      * account. For US bank accounts, this is required and should bethe ACH routing number, not the
@@ -170,12 +224,14 @@ private BankAccount(
         String accountNumber,
         String country,
         String currency,
+        Map<String, Object> extraParams,
         String routingNumber) {
       this.accountHolderName = accountHolderName;
       this.accountHolderType = accountHolderType;
       this.accountNumber = accountNumber;
       this.country = country;
       this.currency = currency;
+      this.extraParams = extraParams;
       this.routingNumber = routingNumber;
     }
 
@@ -194,6 +250,8 @@ public static class Builder {
 
       private String currency;
 
+      private Map<String, Object> extraParams;
+
       private String routingNumber;
 
       /** Finalize and obtain parameter instance from this builder. */
@@ -204,6 +262,7 @@ public BankAccount build() {
             this.accountNumber,
             this.country,
             this.currency,
+            this.extraParams,
             this.routingNumber);
       }
 
@@ -246,6 +305,32 @@ public Builder setCurrency(String currency) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TokenCreateParams.BankAccount#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TokenCreateParams.BankAccount#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * The routing number, sort code, or other country-appropriateinstitution number for the bank
        * account. For US bank accounts, this is required and should bethe ACH routing number, not
@@ -305,6 +390,15 @@ public static class Card {
     @SerializedName("exp_year")
     String expYear;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("name")
     String name;
 
@@ -322,6 +416,7 @@ private Card(
         String cvc,
         String expMonth,
         String expYear,
+        Map<String, Object> extraParams,
         String name,
         String number) {
       this.addressCity = addressCity;
@@ -334,6 +429,7 @@ private Card(
       this.cvc = cvc;
       this.expMonth = expMonth;
       this.expYear = expYear;
+      this.extraParams = extraParams;
       this.name = name;
       this.number = number;
     }
@@ -363,6 +459,8 @@ public static class Builder {
 
       private String expYear;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private String number;
@@ -380,6 +478,7 @@ public Card build() {
             this.cvc,
             this.expMonth,
             this.expYear,
+            this.extraParams,
             this.name,
             this.number);
       }
@@ -434,6 +533,32 @@ public Builder setExpYear(String expYear) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TokenCreateParams.Card#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TokenCreateParams.Card#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       public Builder setName(String name) {
         this.name = name;
         return this;
@@ -447,11 +572,21 @@ public Builder setNumber(String number) {
   }
 
   public static class Pii {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** The `id_number` for the PII, in string form. */
     @SerializedName("id_number")
     String idNumber;
 
-    private Pii(String idNumber) {
+    private Pii(Map<String, Object> extraParams, String idNumber) {
+      this.extraParams = extraParams;
       this.idNumber = idNumber;
     }
 
@@ -460,11 +595,39 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private String idNumber;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Pii build() {
-        return new Pii(this.idNumber);
+        return new Pii(this.extraParams, this.idNumber);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TokenCreateParams.Pii#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TokenCreateParams.Pii#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** The `id_number` for the PII, in string form. */
diff --git a/src/main/java/com/stripe/param/TokenRetrieveParams.java b/src/main/java/com/stripe/param/TokenRetrieveParams.java
index b371aef0e6e..8eb229e46d0 100644
--- a/src/main/java/com/stripe/param/TokenRetrieveParams.java
+++ b/src/main/java/com/stripe/param/TokenRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TokenRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private TokenRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private TokenRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public TokenRetrieveParams build() {
-      return new TokenRetrieveParams(this.expand);
+      return new TokenRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TokenRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TokenRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/TopupCancelParams.java b/src/main/java/com/stripe/param/TopupCancelParams.java
index eec141ec02e..20b5058acd9 100644
--- a/src/main/java/com/stripe/param/TopupCancelParams.java
+++ b/src/main/java/com/stripe/param/TopupCancelParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TopupCancelParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private TopupCancelParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private TopupCancelParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public TopupCancelParams build() {
-      return new TopupCancelParams(this.expand);
+      return new TopupCancelParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TopupCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TopupCancelParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/TopupCreateParams.java b/src/main/java/com/stripe/param/TopupCreateParams.java
index 7fd42be79f4..bfcf75b8147 100644
--- a/src/main/java/com/stripe/param/TopupCreateParams.java
+++ b/src/main/java/com/stripe/param/TopupCreateParams.java
@@ -29,6 +29,15 @@ public class TopupCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -61,6 +70,7 @@ private TopupCreateParams(
       String currency,
       String description,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String source,
       String statementDescriptor,
@@ -69,6 +79,7 @@ private TopupCreateParams(
     this.currency = currency;
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.source = source;
     this.statementDescriptor = statementDescriptor;
@@ -88,6 +99,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String source;
@@ -103,6 +116,7 @@ public TopupCreateParams build() {
           this.currency,
           this.description,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.source,
           this.statementDescriptor,
@@ -156,6 +170,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TopupCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TopupCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/TopupListParams.java b/src/main/java/com/stripe/param/TopupListParams.java
index 88b2515c406..f79c29eadff 100644
--- a/src/main/java/com/stripe/param/TopupListParams.java
+++ b/src/main/java/com/stripe/param/TopupListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class TopupListParams extends ApiRequestParams {
@@ -33,6 +35,15 @@ public class TopupListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -61,6 +72,7 @@ private TopupListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       Status status) {
@@ -68,6 +80,7 @@ private TopupListParams(
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.status = status;
@@ -86,6 +99,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -99,6 +114,7 @@ public TopupListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter,
           this.status);
@@ -171,6 +187,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TopupListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TopupListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -202,6 +244,15 @@ public Builder setStatus(Status status) {
   }
 
   public static class Amount {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -218,7 +269,8 @@ public static class Amount {
     @SerializedName("lte")
     Long lte;
 
-    private Amount(Long gt, Long gte, Long lt, Long lte) {
+    private Amount(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -230,6 +282,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -240,7 +294,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Amount build() {
-        return new Amount(this.gt, this.gte, this.lt, this.lte);
+        return new Amount(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TopupListParams.Amount#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TopupListParams.Amount#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
@@ -270,6 +350,15 @@ public Builder setLte(Long lte) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -286,7 +375,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -298,6 +388,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -308,7 +400,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TopupListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TopupListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/TopupRetrieveParams.java b/src/main/java/com/stripe/param/TopupRetrieveParams.java
index 5b0705dd7b2..83c6713cbc3 100644
--- a/src/main/java/com/stripe/param/TopupRetrieveParams.java
+++ b/src/main/java/com/stripe/param/TopupRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TopupRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private TopupRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private TopupRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public TopupRetrieveParams build() {
-      return new TopupRetrieveParams(this.expand);
+      return new TopupRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TopupRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TopupRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/TopupUpdateParams.java b/src/main/java/com/stripe/param/TopupUpdateParams.java
index d04ab372531..f44d562ad35 100644
--- a/src/main/java/com/stripe/param/TopupUpdateParams.java
+++ b/src/main/java/com/stripe/param/TopupUpdateParams.java
@@ -18,6 +18,15 @@ public class TopupUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format.
@@ -25,9 +34,14 @@ public class TopupUpdateParams extends ApiRequestParams {
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private TopupUpdateParams(String description, List<String> expand, Map<String, String> metadata) {
+  private TopupUpdateParams(
+      String description,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata) {
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -40,11 +54,13 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public TopupUpdateParams build() {
-      return new TopupUpdateParams(this.description, this.expand, this.metadata);
+      return new TopupUpdateParams(this.description, this.expand, this.extraParams, this.metadata);
     }
 
     /** An arbitrary string attached to the object. Often useful for displaying to users. */
@@ -79,6 +95,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TopupUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TopupUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/TransferCreateParams.java b/src/main/java/com/stripe/param/TransferCreateParams.java
index 2972aef8800..1edfe19b511 100644
--- a/src/main/java/com/stripe/param/TransferCreateParams.java
+++ b/src/main/java/com/stripe/param/TransferCreateParams.java
@@ -34,6 +34,15 @@ public class TransferCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -73,6 +82,7 @@ private TransferCreateParams(
       String description,
       String destination,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String sourceTransaction,
       SourceType sourceType,
@@ -82,6 +92,7 @@ private TransferCreateParams(
     this.description = description;
     this.destination = destination;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.sourceTransaction = sourceTransaction;
     this.sourceType = sourceType;
@@ -103,6 +114,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String sourceTransaction;
@@ -119,6 +132,7 @@ public TransferCreateParams build() {
           this.description,
           this.destination,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.sourceTransaction,
           this.sourceType,
@@ -178,6 +192,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransferCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransferCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/TransferListParams.java b/src/main/java/com/stripe/param/TransferListParams.java
index 577bcae59d6..240fb0a5a0a 100644
--- a/src/main/java/com/stripe/param/TransferListParams.java
+++ b/src/main/java/com/stripe/param/TransferListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TransferListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -28,6 +30,15 @@ public class TransferListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -53,6 +64,7 @@ private TransferListParams(
       String destination,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       String transferGroup) {
@@ -60,6 +72,7 @@ private TransferListParams(
     this.destination = destination;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.transferGroup = transferGroup;
@@ -78,6 +91,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -91,6 +106,7 @@ public TransferListParams build() {
           this.destination,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter,
           this.transferGroup);
@@ -149,6 +165,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransferListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransferListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -177,6 +219,15 @@ public Builder setTransferGroup(String transferGroup) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -193,7 +244,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -205,6 +257,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -215,7 +269,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TransferListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TransferListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/TransferRetrieveParams.java b/src/main/java/com/stripe/param/TransferRetrieveParams.java
index 8029685625b..9af0e4bc6f6 100644
--- a/src/main/java/com/stripe/param/TransferRetrieveParams.java
+++ b/src/main/java/com/stripe/param/TransferRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TransferRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private TransferRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private TransferRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public TransferRetrieveParams build() {
-      return new TransferRetrieveParams(this.expand);
+      return new TransferRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransferRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransferRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/TransferReversalCollectionCreateParams.java b/src/main/java/com/stripe/param/TransferReversalCollectionCreateParams.java
index 3ff5b785dae..cdfdb47b438 100644
--- a/src/main/java/com/stripe/param/TransferReversalCollectionCreateParams.java
+++ b/src/main/java/com/stripe/param/TransferReversalCollectionCreateParams.java
@@ -29,6 +29,15 @@ public class TransferReversalCollectionCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -50,11 +59,13 @@ private TransferReversalCollectionCreateParams(
       Long amount,
       String description,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       Boolean refundApplicationFee) {
     this.amount = amount;
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.refundApplicationFee = refundApplicationFee;
   }
@@ -70,6 +81,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private Boolean refundApplicationFee;
@@ -77,7 +90,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public TransferReversalCollectionCreateParams build() {
       return new TransferReversalCollectionCreateParams(
-          this.amount, this.description, this.expand, this.metadata, this.refundApplicationFee);
+          this.amount,
+          this.description,
+          this.expand,
+          this.extraParams,
+          this.metadata,
+          this.refundApplicationFee);
     }
 
     /**
@@ -125,6 +143,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransferReversalCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransferReversalCollectionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/TransferReversalCollectionListParams.java b/src/main/java/com/stripe/param/TransferReversalCollectionListParams.java
index 0aaace5d2b4..87f40a6b5da 100644
--- a/src/main/java/com/stripe/param/TransferReversalCollectionListParams.java
+++ b/src/main/java/com/stripe/param/TransferReversalCollectionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TransferReversalCollectionListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class TransferReversalCollectionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class TransferReversalCollectionListParams extends ApiRequestParams {
   String startingAfter;
 
   private TransferReversalCollectionListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public TransferReversalCollectionListParams build() {
       return new TransferReversalCollectionListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransferReversalCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransferReversalCollectionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/TransferReversalCollectionRetrieveParams.java b/src/main/java/com/stripe/param/TransferReversalCollectionRetrieveParams.java
index 4254b0b76e4..73c252b75db 100644
--- a/src/main/java/com/stripe/param/TransferReversalCollectionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/TransferReversalCollectionRetrieveParams.java
@@ -5,15 +5,28 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TransferReversalCollectionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private TransferReversalCollectionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private TransferReversalCollectionRetrieveParams(
+      List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +36,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public TransferReversalCollectionRetrieveParams build() {
-      return new TransferReversalCollectionRetrieveParams(this.expand);
+      return new TransferReversalCollectionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +68,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransferReversalCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransferReversalCollectionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/TransferReversalUpdateParams.java b/src/main/java/com/stripe/param/TransferReversalUpdateParams.java
index 7919a12baa4..2f4a25f034e 100644
--- a/src/main/java/com/stripe/param/TransferReversalUpdateParams.java
+++ b/src/main/java/com/stripe/param/TransferReversalUpdateParams.java
@@ -14,6 +14,15 @@ public class TransferReversalUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -22,8 +31,10 @@ public class TransferReversalUpdateParams extends ApiRequestParams {
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private TransferReversalUpdateParams(List<String> expand, Map<String, String> metadata) {
+  private TransferReversalUpdateParams(
+      List<String> expand, Map<String, Object> extraParams, Map<String, String> metadata) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -34,11 +45,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public TransferReversalUpdateParams build() {
-      return new TransferReversalUpdateParams(this.expand, this.metadata);
+      return new TransferReversalUpdateParams(this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -67,6 +80,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransferReversalUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransferReversalUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/TransferUpdateParams.java b/src/main/java/com/stripe/param/TransferUpdateParams.java
index b2cb0c3e04c..e925869c38c 100644
--- a/src/main/java/com/stripe/param/TransferUpdateParams.java
+++ b/src/main/java/com/stripe/param/TransferUpdateParams.java
@@ -18,6 +18,15 @@ public class TransferUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -27,9 +36,13 @@ public class TransferUpdateParams extends ApiRequestParams {
   Map<String, String> metadata;
 
   private TransferUpdateParams(
-      String description, List<String> expand, Map<String, String> metadata) {
+      String description,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata) {
     this.description = description;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -42,11 +55,14 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public TransferUpdateParams build() {
-      return new TransferUpdateParams(this.description, this.expand, this.metadata);
+      return new TransferUpdateParams(
+          this.description, this.expand, this.extraParams, this.metadata);
     }
 
     /** An arbitrary string attached to the object. Often useful for displaying to users. */
@@ -81,6 +97,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransferUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransferUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/UsageRecordCreateOnSubscriptionItemParams.java b/src/main/java/com/stripe/param/UsageRecordCreateOnSubscriptionItemParams.java
index db555aa8f48..690dff5c65e 100644
--- a/src/main/java/com/stripe/param/UsageRecordCreateOnSubscriptionItemParams.java
+++ b/src/main/java/com/stripe/param/UsageRecordCreateOnSubscriptionItemParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class UsageRecordCreateOnSubscriptionItemParams extends ApiRequestParams {
@@ -23,6 +25,15 @@ public class UsageRecordCreateOnSubscriptionItemParams extends ApiRequestParams
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The usage quantity for the specified timestamp. */
   @SerializedName("quantity")
   Long quantity;
@@ -35,9 +46,14 @@ public class UsageRecordCreateOnSubscriptionItemParams extends ApiRequestParams
   Long timestamp;
 
   private UsageRecordCreateOnSubscriptionItemParams(
-      Action action, List<String> expand, Long quantity, Long timestamp) {
+      Action action,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long quantity,
+      Long timestamp) {
     this.action = action;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.quantity = quantity;
     this.timestamp = timestamp;
   }
@@ -51,6 +67,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long quantity;
 
     private Long timestamp;
@@ -58,7 +76,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public UsageRecordCreateOnSubscriptionItemParams build() {
       return new UsageRecordCreateOnSubscriptionItemParams(
-          this.action, this.expand, this.quantity, this.timestamp);
+          this.action, this.expand, this.extraParams, this.quantity, this.timestamp);
     }
 
     /**
@@ -99,6 +117,33 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * UsageRecordCreateOnSubscriptionItemParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link UsageRecordCreateOnSubscriptionItemParams#extraParams} for the field
+     * documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The usage quantity for the specified timestamp. */
     public Builder setQuantity(Long quantity) {
       this.quantity = quantity;
diff --git a/src/main/java/com/stripe/param/WebhookEndpointCreateParams.java b/src/main/java/com/stripe/param/WebhookEndpointCreateParams.java
index 8e02aa3341a..e28fa7df7b9 100644
--- a/src/main/java/com/stripe/param/WebhookEndpointCreateParams.java
+++ b/src/main/java/com/stripe/param/WebhookEndpointCreateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class WebhookEndpointCreateParams extends ApiRequestParams {
@@ -33,6 +35,15 @@ public class WebhookEndpointCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The URL of the webhook endpoint. */
   @SerializedName("url")
   String url;
@@ -42,11 +53,13 @@ private WebhookEndpointCreateParams(
       Boolean connect,
       List<EnabledEvent> enabledEvents,
       List<String> expand,
+      Map<String, Object> extraParams,
       String url) {
     this.apiVersion = apiVersion;
     this.connect = connect;
     this.enabledEvents = enabledEvents;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.url = url;
   }
 
@@ -63,12 +76,19 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String url;
 
     /** Finalize and obtain parameter instance from this builder. */
     public WebhookEndpointCreateParams build() {
       return new WebhookEndpointCreateParams(
-          this.apiVersion, this.connect, this.enabledEvents, this.expand, this.url);
+          this.apiVersion,
+          this.connect,
+          this.enabledEvents,
+          this.expand,
+          this.extraParams,
+          this.url);
     }
 
     /**
@@ -141,6 +161,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * WebhookEndpointCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link WebhookEndpointCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The URL of the webhook endpoint. */
     public Builder setUrl(String url) {
       this.url = url;
@@ -683,6 +729,9 @@ public enum EnabledEvent implements ApiRequestParams.EnumParam {
     @SerializedName("payment_method.detached")
     PAYMENT_METHOD__DETACHED("payment_method.detached"),
 
+    @SerializedName("payment_method.updated")
+    PAYMENT_METHOD__UPDATED("payment_method.updated"),
+
     @SerializedName("payout.canceled")
     PAYOUT__CANCELED("payout.canceled"),
 
diff --git a/src/main/java/com/stripe/param/WebhookEndpointListParams.java b/src/main/java/com/stripe/param/WebhookEndpointListParams.java
index f5a1e0cbf16..a8aeda835df 100644
--- a/src/main/java/com/stripe/param/WebhookEndpointListParams.java
+++ b/src/main/java/com/stripe/param/WebhookEndpointListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class WebhookEndpointListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class WebhookEndpointListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class WebhookEndpointListParams extends ApiRequestParams {
   String startingAfter;
 
   private WebhookEndpointListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public WebhookEndpointListParams build() {
       return new WebhookEndpointListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * WebhookEndpointListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link WebhookEndpointListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/WebhookEndpointRetrieveParams.java b/src/main/java/com/stripe/param/WebhookEndpointRetrieveParams.java
index 9143e8949b5..226c7b46ab2 100644
--- a/src/main/java/com/stripe/param/WebhookEndpointRetrieveParams.java
+++ b/src/main/java/com/stripe/param/WebhookEndpointRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class WebhookEndpointRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private WebhookEndpointRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private WebhookEndpointRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public WebhookEndpointRetrieveParams build() {
-      return new WebhookEndpointRetrieveParams(this.expand);
+      return new WebhookEndpointRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * WebhookEndpointRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link WebhookEndpointRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/WebhookEndpointUpdateParams.java b/src/main/java/com/stripe/param/WebhookEndpointUpdateParams.java
index b6ab8f6934d..e1cca7d5ae8 100644
--- a/src/main/java/com/stripe/param/WebhookEndpointUpdateParams.java
+++ b/src/main/java/com/stripe/param/WebhookEndpointUpdateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class WebhookEndpointUpdateParams extends ApiRequestParams {
@@ -23,15 +25,29 @@ public class WebhookEndpointUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The URL of the webhook endpoint. */
   @SerializedName("url")
   String url;
 
   private WebhookEndpointUpdateParams(
-      Boolean disabled, List<EnabledEvent> enabledEvents, List<String> expand, String url) {
+      Boolean disabled,
+      List<EnabledEvent> enabledEvents,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      String url) {
     this.disabled = disabled;
     this.enabledEvents = enabledEvents;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.url = url;
   }
 
@@ -46,12 +62,14 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String url;
 
     /** Finalize and obtain parameter instance from this builder. */
     public WebhookEndpointUpdateParams build() {
       return new WebhookEndpointUpdateParams(
-          this.disabled, this.enabledEvents, this.expand, this.url);
+          this.disabled, this.enabledEvents, this.expand, this.extraParams, this.url);
     }
 
     /** Disable the webhook endpoint if set to true. */
@@ -112,6 +130,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * WebhookEndpointUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link WebhookEndpointUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The URL of the webhook endpoint. */
     public Builder setUrl(String url) {
       this.url = url;
@@ -384,6 +428,9 @@ public enum EnabledEvent implements ApiRequestParams.EnumParam {
     @SerializedName("payment_method.detached")
     PAYMENT_METHOD__DETACHED("payment_method.detached"),
 
+    @SerializedName("payment_method.updated")
+    PAYMENT_METHOD__UPDATED("payment_method.updated"),
+
     @SerializedName("payout.canceled")
     PAYOUT__CANCELED("payout.canceled"),
 
diff --git a/src/main/java/com/stripe/param/checkout/SessionCreateParams.java b/src/main/java/com/stripe/param/checkout/SessionCreateParams.java
index b3b8f016d78..d2ef1e2b3c4 100644
--- a/src/main/java/com/stripe/param/checkout/SessionCreateParams.java
+++ b/src/main/java/com/stripe/param/checkout/SessionCreateParams.java
@@ -56,6 +56,15 @@ public class SessionCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A list of items the customer is purchasing. Use this parameter for one-time payments. To create
    * subscriptions, use `subscription_data.items`.
@@ -100,6 +109,7 @@ private SessionCreateParams(
       String customer,
       String customerEmail,
       List<String> expand,
+      Map<String, Object> extraParams,
       List<LineItem> lineItems,
       Locale locale,
       PaymentIntentData paymentIntentData,
@@ -112,6 +122,7 @@ private SessionCreateParams(
     this.customer = customer;
     this.customerEmail = customerEmail;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.lineItems = lineItems;
     this.locale = locale;
     this.paymentIntentData = paymentIntentData;
@@ -137,6 +148,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private List<LineItem> lineItems;
 
     private Locale locale;
@@ -158,6 +171,7 @@ public SessionCreateParams build() {
           this.customer,
           this.customerEmail,
           this.expand,
+          this.extraParams,
           this.lineItems,
           this.locale,
           this.paymentIntentData,
@@ -244,6 +258,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SessionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SessionCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add an element to `lineItems` list. A list is initialized for the first `add/addAll` call,
      * and subsequent calls adds additional elements to the original list. See {@link
@@ -344,6 +384,15 @@ public static class LineItem {
     @SerializedName("description")
     String description;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** A list of images representing this line item. */
     @SerializedName("images")
     List<String> images;
@@ -360,12 +409,14 @@ private LineItem(
         Long amount,
         String currency,
         String description,
+        Map<String, Object> extraParams,
         List<String> images,
         String name,
         Long quantity) {
       this.amount = amount;
       this.currency = currency;
       this.description = description;
+      this.extraParams = extraParams;
       this.images = images;
       this.name = name;
       this.quantity = quantity;
@@ -382,6 +433,8 @@ public static class Builder {
 
       private String description;
 
+      private Map<String, Object> extraParams;
+
       private List<String> images;
 
       private String name;
@@ -391,7 +444,13 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public LineItem build() {
         return new LineItem(
-            this.amount, this.currency, this.description, this.images, this.name, this.quantity);
+            this.amount,
+            this.currency,
+            this.description,
+            this.extraParams,
+            this.images,
+            this.name,
+            this.quantity);
       }
 
       /** The amount to be collected per unit of the line item. */
@@ -415,6 +474,32 @@ public Builder setDescription(String description) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SessionCreateParams.LineItem#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SessionCreateParams.LineItem#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Add an element to `images` list. A list is initialized for the first `add/addAll` call, and
        * subsequent calls adds additional elements to the original list. See {@link
@@ -474,6 +559,15 @@ public static class PaymentIntentData {
     @SerializedName("description")
     String description;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Set of key-value pairs that you can attach to an object. This can be useful for storing
      * additional information about the object in a structured format.
@@ -515,6 +609,7 @@ private PaymentIntentData(
         Long applicationFeeAmount,
         CaptureMethod captureMethod,
         String description,
+        Map<String, Object> extraParams,
         Map<String, String> metadata,
         String onBehalfOf,
         String receiptEmail,
@@ -524,6 +619,7 @@ private PaymentIntentData(
       this.applicationFeeAmount = applicationFeeAmount;
       this.captureMethod = captureMethod;
       this.description = description;
+      this.extraParams = extraParams;
       this.metadata = metadata;
       this.onBehalfOf = onBehalfOf;
       this.receiptEmail = receiptEmail;
@@ -543,6 +639,8 @@ public static class Builder {
 
       private String description;
 
+      private Map<String, Object> extraParams;
+
       private Map<String, String> metadata;
 
       private String onBehalfOf;
@@ -561,6 +659,7 @@ public PaymentIntentData build() {
             this.applicationFeeAmount,
             this.captureMethod,
             this.description,
+            this.extraParams,
             this.metadata,
             this.onBehalfOf,
             this.receiptEmail,
@@ -593,6 +692,32 @@ public Builder setDescription(String description) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SessionCreateParams.PaymentIntentData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SessionCreateParams.PaymentIntentData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll`
        * call, and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -670,6 +795,15 @@ public static class Shipping {
       @SerializedName("carrier")
       String carrier;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Recipient name. */
       @SerializedName("name")
       String name;
@@ -686,9 +820,15 @@ public static class Shipping {
       String trackingNumber;
 
       private Shipping(
-          Address address, String carrier, String name, String phone, String trackingNumber) {
+          Address address,
+          String carrier,
+          Map<String, Object> extraParams,
+          String name,
+          String phone,
+          String trackingNumber) {
         this.address = address;
         this.carrier = carrier;
+        this.extraParams = extraParams;
         this.name = name;
         this.phone = phone;
         this.trackingNumber = trackingNumber;
@@ -704,6 +844,8 @@ public static class Builder {
 
         private String carrier;
 
+        private Map<String, Object> extraParams;
+
         private String name;
 
         private String phone;
@@ -713,7 +855,12 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Shipping build() {
           return new Shipping(
-              this.address, this.carrier, this.name, this.phone, this.trackingNumber);
+              this.address,
+              this.carrier,
+              this.extraParams,
+              this.name,
+              this.phone,
+              this.trackingNumber);
         }
 
         /** Shipping address. */
@@ -728,6 +875,34 @@ public Builder setCarrier(String carrier) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SessionCreateParams.PaymentIntentData.Shipping#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SessionCreateParams.PaymentIntentData.Shipping#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /** Recipient name. */
         public Builder setName(String name) {
           this.name = name;
@@ -758,6 +933,16 @@ public static class Address {
         @SerializedName("country")
         String country;
 
+        /**
+         * Map of extra parameters for custom features not available in this client library. The
+         * content in this map is not serialized under this field's {@code @SerializedName} value.
+         * Instead, each key/value pair is serialized as if the key is a root-level field
+         * (serialized) name in this param object. Effectively, this map is flattened to its parent
+         * instance.
+         */
+        @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+        Map<String, Object> extraParams;
+
         @SerializedName("line1")
         String line1;
 
@@ -773,12 +958,14 @@ public static class Address {
         private Address(
             String city,
             String country,
+            Map<String, Object> extraParams,
             String line1,
             String line2,
             String postalCode,
             String state) {
           this.city = city;
           this.country = country;
+          this.extraParams = extraParams;
           this.line1 = line1;
           this.line2 = line2;
           this.postalCode = postalCode;
@@ -795,6 +982,8 @@ public static class Builder {
 
           private String country;
 
+          private Map<String, Object> extraParams;
+
           private String line1;
 
           private String line2;
@@ -806,7 +995,13 @@ public static class Builder {
           /** Finalize and obtain parameter instance from this builder. */
           public Address build() {
             return new Address(
-                this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+                this.city,
+                this.country,
+                this.extraParams,
+                this.line1,
+                this.line2,
+                this.postalCode,
+                this.state);
           }
 
           public Builder setCity(String city) {
@@ -819,6 +1014,34 @@ public Builder setCountry(String country) {
             return this;
           }
 
+          /**
+           * Add a key/value pair to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link SessionCreateParams.PaymentIntentData.Shipping.Address#extraParams} for
+           * the field documentation.
+           */
+          public Builder putExtraParam(String key, Object value) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.put(key, value);
+            return this;
+          }
+
+          /**
+           * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+           * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+           * map. See {@link SessionCreateParams.PaymentIntentData.Shipping.Address#extraParams} for
+           * the field documentation.
+           */
+          public Builder putAllExtraParam(Map<String, Object> map) {
+            if (this.extraParams == null) {
+              this.extraParams = new HashMap<>();
+            }
+            this.extraParams.putAll(map);
+            return this;
+          }
+
           public Builder setLine1(String line1) {
             this.line1 = line1;
             return this;
@@ -851,8 +1074,18 @@ public static class TransferData {
       @SerializedName("destination")
       String destination;
 
-      private TransferData(String destination) {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
+      private TransferData(String destination, Map<String, Object> extraParams) {
         this.destination = destination;
+        this.extraParams = extraParams;
       }
 
       public static Builder builder() {
@@ -863,9 +1096,11 @@ public static Builder builder() {
       public static class Builder {
         private String destination;
 
+        private Map<String, Object> extraParams;
+
         /** Finalize and obtain parameter instance from this builder. */
         public TransferData build() {
-          return new TransferData(this.destination);
+          return new TransferData(this.destination, this.extraParams);
         }
 
         /**
@@ -878,6 +1113,34 @@ public Builder setDestination(String destination) {
           this.destination = destination;
           return this;
         }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SessionCreateParams.PaymentIntentData.TransferData#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SessionCreateParams.PaymentIntentData.TransferData#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
       }
     }
 
@@ -898,6 +1161,15 @@ public enum CaptureMethod implements ApiRequestParams.EnumParam {
   }
 
   public static class SubscriptionData {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * A list of items, each with an attached plan, that the customer is subscribing to. Use this
      * parameter for subscriptions. To create one-time payments, use `line_items`.
@@ -927,7 +1199,12 @@ public static class SubscriptionData {
     Long trialPeriodDays;
 
     private SubscriptionData(
-        List<Item> items, Map<String, String> metadata, Long trialEnd, Long trialPeriodDays) {
+        Map<String, Object> extraParams,
+        List<Item> items,
+        Map<String, String> metadata,
+        Long trialEnd,
+        Long trialPeriodDays) {
+      this.extraParams = extraParams;
       this.items = items;
       this.metadata = metadata;
       this.trialEnd = trialEnd;
@@ -939,6 +1216,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private List<Item> items;
 
       private Map<String, String> metadata;
@@ -949,7 +1228,34 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public SubscriptionData build() {
-        return new SubscriptionData(this.items, this.metadata, this.trialEnd, this.trialPeriodDays);
+        return new SubscriptionData(
+            this.extraParams, this.items, this.metadata, this.trialEnd, this.trialPeriodDays);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * SessionCreateParams.SubscriptionData#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link SessionCreateParams.SubscriptionData#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /**
@@ -1024,6 +1330,15 @@ public Builder setTrialPeriodDays(Long trialPeriodDays) {
     }
 
     public static class Item {
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /** Plan ID for this item. */
       @SerializedName("plan")
       String plan;
@@ -1032,7 +1347,8 @@ public static class Item {
       @SerializedName("quantity")
       Long quantity;
 
-      private Item(String plan, Long quantity) {
+      private Item(Map<String, Object> extraParams, String plan, Long quantity) {
+        this.extraParams = extraParams;
         this.plan = plan;
         this.quantity = quantity;
       }
@@ -1042,13 +1358,43 @@ public static Builder builder() {
       }
 
       public static class Builder {
+        private Map<String, Object> extraParams;
+
         private String plan;
 
         private Long quantity;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Item build() {
-          return new Item(this.plan, this.quantity);
+          return new Item(this.extraParams, this.plan, this.quantity);
+        }
+
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SessionCreateParams.SubscriptionData.Item#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link SessionCreateParams.SubscriptionData.Item#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
         }
 
         /** Plan ID for this item. */
diff --git a/src/main/java/com/stripe/param/checkout/SessionRetrieveParams.java b/src/main/java/com/stripe/param/checkout/SessionRetrieveParams.java
index 07f93856de1..15673570c28 100644
--- a/src/main/java/com/stripe/param/checkout/SessionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/checkout/SessionRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class SessionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private SessionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private SessionRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public SessionRetrieveParams build() {
-      return new SessionRetrieveParams(this.expand);
+      return new SessionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * SessionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link SessionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/issuing/AuthorizationApproveParams.java b/src/main/java/com/stripe/param/issuing/AuthorizationApproveParams.java
index e01ef0c66b2..d9ab59475f1 100644
--- a/src/main/java/com/stripe/param/issuing/AuthorizationApproveParams.java
+++ b/src/main/java/com/stripe/param/issuing/AuthorizationApproveParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class AuthorizationApproveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * If the authorization's `is_held_amount_controllable` property is `true`, you may provide this
    * value to control how much to hold for the authorization. Must be positive (use
@@ -21,8 +32,10 @@ public class AuthorizationApproveParams extends ApiRequestParams {
   @SerializedName("held_amount")
   Long heldAmount;
 
-  private AuthorizationApproveParams(List<String> expand, Long heldAmount) {
+  private AuthorizationApproveParams(
+      List<String> expand, Map<String, Object> extraParams, Long heldAmount) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.heldAmount = heldAmount;
   }
 
@@ -33,11 +46,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long heldAmount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public AuthorizationApproveParams build() {
-      return new AuthorizationApproveParams(this.expand, this.heldAmount);
+      return new AuthorizationApproveParams(this.expand, this.extraParams, this.heldAmount);
     }
 
     /**
@@ -66,6 +81,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AuthorizationApproveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AuthorizationApproveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * If the authorization's `is_held_amount_controllable` property is `true`, you may provide this
      * value to control how much to hold for the authorization. Must be positive (use
diff --git a/src/main/java/com/stripe/param/issuing/AuthorizationDeclineParams.java b/src/main/java/com/stripe/param/issuing/AuthorizationDeclineParams.java
index 02a81494289..b9492a847e8 100644
--- a/src/main/java/com/stripe/param/issuing/AuthorizationDeclineParams.java
+++ b/src/main/java/com/stripe/param/issuing/AuthorizationDeclineParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class AuthorizationDeclineParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private AuthorizationDeclineParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private AuthorizationDeclineParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public AuthorizationDeclineParams build() {
-      return new AuthorizationDeclineParams(this.expand);
+      return new AuthorizationDeclineParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AuthorizationDeclineParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AuthorizationDeclineParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/issuing/AuthorizationListParams.java b/src/main/java/com/stripe/param/issuing/AuthorizationListParams.java
index 79f70f7f9ea..9dd317c962d 100644
--- a/src/main/java/com/stripe/param/issuing/AuthorizationListParams.java
+++ b/src/main/java/com/stripe/param/issuing/AuthorizationListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class AuthorizationListParams extends ApiRequestParams {
@@ -34,6 +36,15 @@ public class AuthorizationListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -60,6 +71,7 @@ private AuthorizationListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       Status status) {
@@ -68,6 +80,7 @@ private AuthorizationListParams(
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.status = status;
@@ -88,6 +101,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -102,6 +117,7 @@ public AuthorizationListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter,
           this.status);
@@ -168,6 +184,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AuthorizationListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AuthorizationListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -196,6 +238,15 @@ public Builder setStatus(Status status) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -212,7 +263,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -224,6 +276,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -234,7 +288,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * AuthorizationListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link AuthorizationListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/issuing/AuthorizationRetrieveParams.java b/src/main/java/com/stripe/param/issuing/AuthorizationRetrieveParams.java
index 2cc2dec7d38..5b035c49eae 100644
--- a/src/main/java/com/stripe/param/issuing/AuthorizationRetrieveParams.java
+++ b/src/main/java/com/stripe/param/issuing/AuthorizationRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class AuthorizationRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private AuthorizationRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private AuthorizationRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public AuthorizationRetrieveParams build() {
-      return new AuthorizationRetrieveParams(this.expand);
+      return new AuthorizationRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AuthorizationRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AuthorizationRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/issuing/AuthorizationUpdateParams.java b/src/main/java/com/stripe/param/issuing/AuthorizationUpdateParams.java
index 776b50aeff6..343775c88e8 100644
--- a/src/main/java/com/stripe/param/issuing/AuthorizationUpdateParams.java
+++ b/src/main/java/com/stripe/param/issuing/AuthorizationUpdateParams.java
@@ -14,11 +14,22 @@ public class AuthorizationUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private AuthorizationUpdateParams(List<String> expand, Map<String, String> metadata) {
+  private AuthorizationUpdateParams(
+      List<String> expand, Map<String, Object> extraParams, Map<String, String> metadata) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -29,11 +40,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public AuthorizationUpdateParams build() {
-      return new AuthorizationUpdateParams(this.expand, this.metadata);
+      return new AuthorizationUpdateParams(this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -62,6 +75,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * AuthorizationUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link AuthorizationUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/issuing/CardCreateParams.java b/src/main/java/com/stripe/param/issuing/CardCreateParams.java
index 226a0b41f95..20980c13c73 100644
--- a/src/main/java/com/stripe/param/issuing/CardCreateParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardCreateParams.java
@@ -35,6 +35,15 @@ public class CardCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
@@ -69,6 +78,7 @@ private CardCreateParams(
       String cardholder,
       String currency,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       String replacementFor,
       ReplacementReason replacementReason,
@@ -79,6 +89,7 @@ private CardCreateParams(
     this.cardholder = cardholder;
     this.currency = currency;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.replacementFor = replacementFor;
     this.replacementReason = replacementReason;
@@ -100,6 +111,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String replacementFor;
@@ -119,6 +132,7 @@ public CardCreateParams build() {
           this.cardholder,
           this.currency,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.replacementFor,
           this.replacementReason,
@@ -178,6 +192,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -258,6 +298,15 @@ public static class AuthorizationControls {
     @SerializedName("blocked_categories")
     List<BlockedCategory> blockedCategories;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Maximum amount allowed per authorization on this card, in the currency of the card.
      * Authorization amounts in a different currency will be converted to the card's currency when
@@ -280,11 +329,13 @@ public static class AuthorizationControls {
     private AuthorizationControls(
         List<AllowedCategory> allowedCategories,
         List<BlockedCategory> blockedCategories,
+        Map<String, Object> extraParams,
         Long maxAmount,
         Long maxApprovals,
         List<SpendingLimit> spendingLimits) {
       this.allowedCategories = allowedCategories;
       this.blockedCategories = blockedCategories;
+      this.extraParams = extraParams;
       this.maxAmount = maxAmount;
       this.maxApprovals = maxApprovals;
       this.spendingLimits = spendingLimits;
@@ -299,6 +350,8 @@ public static class Builder {
 
       private List<BlockedCategory> blockedCategories;
 
+      private Map<String, Object> extraParams;
+
       private Long maxAmount;
 
       private Long maxApprovals;
@@ -310,6 +363,7 @@ public AuthorizationControls build() {
         return new AuthorizationControls(
             this.allowedCategories,
             this.blockedCategories,
+            this.extraParams,
             this.maxAmount,
             this.maxApprovals,
             this.spendingLimits);
@@ -357,6 +411,32 @@ public Builder addAllBlockedCategory(List<BlockedCategory> elements) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardCreateParams.AuthorizationControls#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardCreateParams.AuthorizationControls#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Maximum amount allowed per authorization on this card, in the currency of the card.
        * Authorization amounts in a different currency will be converted to the card's currency when
@@ -430,6 +510,15 @@ public static class SpendingLimit {
       @SerializedName("categories")
       List<Category> categories;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The time interval with which to apply this spending limit towards. Allowed values are
        * 'per_authorization', 'daily', 'weekly', 'monthly', 'yearly', and 'all_time'.
@@ -437,9 +526,14 @@ public static class SpendingLimit {
       @SerializedName("interval")
       Interval interval;
 
-      private SpendingLimit(Long amount, List<Category> categories, Interval interval) {
+      private SpendingLimit(
+          Long amount,
+          List<Category> categories,
+          Map<String, Object> extraParams,
+          Interval interval) {
         this.amount = amount;
         this.categories = categories;
+        this.extraParams = extraParams;
         this.interval = interval;
       }
 
@@ -453,11 +547,13 @@ public static class Builder {
 
         private List<Category> categories;
 
+        private Map<String, Object> extraParams;
+
         private Interval interval;
 
         /** Finalize and obtain parameter instance from this builder. */
         public SpendingLimit build() {
-          return new SpendingLimit(this.amount, this.categories, this.interval);
+          return new SpendingLimit(this.amount, this.categories, this.extraParams, this.interval);
         }
 
         /** Maximum amount allowed to spend per time interval. */
@@ -494,6 +590,34 @@ public Builder addAllCategory(List<Category> elements) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardCreateParams.AuthorizationControls.SpendingLimit#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardCreateParams.AuthorizationControls.SpendingLimit#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * The time interval with which to apply this spending limit towards. Allowed values are
          * 'per_authorization', 'daily', 'weekly', 'monthly', 'yearly', and 'all_time'.
@@ -3180,6 +3304,15 @@ public static class Shipping {
     @SerializedName("address")
     Address address;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("name")
     String name;
 
@@ -3190,8 +3323,13 @@ public static class Shipping {
     @SerializedName("type")
     ApiRequestParams.EnumParam type;
 
-    private Shipping(Address address, String name, ApiRequestParams.EnumParam type) {
+    private Shipping(
+        Address address,
+        Map<String, Object> extraParams,
+        String name,
+        ApiRequestParams.EnumParam type) {
       this.address = address;
+      this.extraParams = extraParams;
       this.name = name;
       this.type = type;
     }
@@ -3203,13 +3341,15 @@ public static Builder builder() {
     public static class Builder {
       private Address address;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       private ApiRequestParams.EnumParam type;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Shipping build() {
-        return new Shipping(this.address, this.name, this.type);
+        return new Shipping(this.address, this.extraParams, this.name, this.type);
       }
 
       public Builder setAddress(Address address) {
@@ -3217,6 +3357,32 @@ public Builder setAddress(Address address) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardCreateParams.Shipping#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       public Builder setName(String name) {
         this.name = name;
         return this;
@@ -3248,6 +3414,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -3263,12 +3438,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -3284,6 +3461,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -3295,7 +3474,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -3308,6 +3493,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardCreateParams.Shipping.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
diff --git a/src/main/java/com/stripe/param/issuing/CardDetailsParams.java b/src/main/java/com/stripe/param/issuing/CardDetailsParams.java
index 10576977ebf..14bc101178d 100644
--- a/src/main/java/com/stripe/param/issuing/CardDetailsParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardDetailsParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CardDetailsParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private CardDetailsParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private CardDetailsParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public CardDetailsParams build() {
-      return new CardDetailsParams(this.expand);
+      return new CardDetailsParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardDetailsParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardDetailsParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/issuing/CardListParams.java b/src/main/java/com/stripe/param/issuing/CardListParams.java
index 782aaded0aa..2fb6b779e54 100644
--- a/src/main/java/com/stripe/param/issuing/CardListParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class CardListParams extends ApiRequestParams {
@@ -38,6 +40,15 @@ public class CardListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Only return cards that have the given last four digits. */
   @SerializedName("last4")
   String last4;
@@ -84,6 +95,7 @@ private CardListParams(
       Long expMonth,
       Long expYear,
       List<String> expand,
+      Map<String, Object> extraParams,
       String last4,
       Long limit,
       String name,
@@ -97,6 +109,7 @@ private CardListParams(
     this.expMonth = expMonth;
     this.expYear = expYear;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.last4 = last4;
     this.limit = limit;
     this.name = name;
@@ -123,6 +136,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String last4;
 
     private Long limit;
@@ -146,6 +161,7 @@ public CardListParams build() {
           this.expMonth,
           this.expYear,
           this.expand,
+          this.extraParams,
           this.last4,
           this.limit,
           this.name,
@@ -222,6 +238,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Only return cards that have the given last four digits. */
     public Builder setLast4(String last4) {
       this.last4 = last4;
@@ -277,6 +319,15 @@ public Builder setType(Type type) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -293,7 +344,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -305,6 +357,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -315,7 +369,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/issuing/CardRetrieveParams.java b/src/main/java/com/stripe/param/issuing/CardRetrieveParams.java
index 7fe334d2acb..6a88a854ab3 100644
--- a/src/main/java/com/stripe/param/issuing/CardRetrieveParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CardRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private CardRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private CardRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public CardRetrieveParams build() {
-      return new CardRetrieveParams(this.expand);
+      return new CardRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/issuing/CardUpdateParams.java b/src/main/java/com/stripe/param/issuing/CardUpdateParams.java
index a64c6056361..0c499f07439 100644
--- a/src/main/java/com/stripe/param/issuing/CardUpdateParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardUpdateParams.java
@@ -30,6 +30,15 @@ public class CardUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
@@ -44,11 +53,13 @@ private CardUpdateParams(
       AuthorizationControls authorizationControls,
       String cardholder,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       Status status) {
     this.authorizationControls = authorizationControls;
     this.cardholder = cardholder;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.status = status;
   }
@@ -64,6 +75,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private Status status;
@@ -71,7 +84,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public CardUpdateParams build() {
       return new CardUpdateParams(
-          this.authorizationControls, this.cardholder, this.expand, this.metadata, this.status);
+          this.authorizationControls,
+          this.cardholder,
+          this.expand,
+          this.extraParams,
+          this.metadata,
+          this.status);
     }
 
     /**
@@ -119,6 +137,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -172,6 +216,15 @@ public static class AuthorizationControls {
     @SerializedName("blocked_categories")
     List<BlockedCategory> blockedCategories;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Maximum amount allowed per authorization on this card, in the currency of the card.
      * Authorization amounts in a different currency will be converted to the card's currency when
@@ -194,11 +247,13 @@ public static class AuthorizationControls {
     private AuthorizationControls(
         List<AllowedCategory> allowedCategories,
         List<BlockedCategory> blockedCategories,
+        Map<String, Object> extraParams,
         Long maxAmount,
         Long maxApprovals,
         List<SpendingLimit> spendingLimits) {
       this.allowedCategories = allowedCategories;
       this.blockedCategories = blockedCategories;
+      this.extraParams = extraParams;
       this.maxAmount = maxAmount;
       this.maxApprovals = maxApprovals;
       this.spendingLimits = spendingLimits;
@@ -213,6 +268,8 @@ public static class Builder {
 
       private List<BlockedCategory> blockedCategories;
 
+      private Map<String, Object> extraParams;
+
       private Long maxAmount;
 
       private Long maxApprovals;
@@ -224,6 +281,7 @@ public AuthorizationControls build() {
         return new AuthorizationControls(
             this.allowedCategories,
             this.blockedCategories,
+            this.extraParams,
             this.maxAmount,
             this.maxApprovals,
             this.spendingLimits);
@@ -271,6 +329,32 @@ public Builder addAllBlockedCategory(List<BlockedCategory> elements) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardUpdateParams.AuthorizationControls#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardUpdateParams.AuthorizationControls#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Maximum amount allowed per authorization on this card, in the currency of the card.
        * Authorization amounts in a different currency will be converted to the card's currency when
@@ -344,6 +428,15 @@ public static class SpendingLimit {
       @SerializedName("categories")
       List<Category> categories;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The time interval with which to apply this spending limit towards. Allowed values are
        * 'per_authorization', 'daily', 'weekly', 'monthly', 'yearly', and 'all_time'.
@@ -351,9 +444,14 @@ public static class SpendingLimit {
       @SerializedName("interval")
       Interval interval;
 
-      private SpendingLimit(Long amount, List<Category> categories, Interval interval) {
+      private SpendingLimit(
+          Long amount,
+          List<Category> categories,
+          Map<String, Object> extraParams,
+          Interval interval) {
         this.amount = amount;
         this.categories = categories;
+        this.extraParams = extraParams;
         this.interval = interval;
       }
 
@@ -367,11 +465,13 @@ public static class Builder {
 
         private List<Category> categories;
 
+        private Map<String, Object> extraParams;
+
         private Interval interval;
 
         /** Finalize and obtain parameter instance from this builder. */
         public SpendingLimit build() {
-          return new SpendingLimit(this.amount, this.categories, this.interval);
+          return new SpendingLimit(this.amount, this.categories, this.extraParams, this.interval);
         }
 
         /** Maximum amount allowed to spend per time interval. */
@@ -408,6 +508,34 @@ public Builder addAllCategory(List<Category> elements) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardUpdateParams.AuthorizationControls.SpendingLimit#extraParams} for the
+         * field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardUpdateParams.AuthorizationControls.SpendingLimit#extraParams} for the
+         * field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * The time interval with which to apply this spending limit towards. Allowed values are
          * 'per_authorization', 'daily', 'weekly', 'monthly', 'yearly', and 'all_time'.
diff --git a/src/main/java/com/stripe/param/issuing/CardholderCreateParams.java b/src/main/java/com/stripe/param/issuing/CardholderCreateParams.java
index 3510f15d535..790d267bc9a 100644
--- a/src/main/java/com/stripe/param/issuing/CardholderCreateParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardholderCreateParams.java
@@ -31,6 +31,15 @@ public class CardholderCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Specifies whether to set this as the default cardholder. */
   @SerializedName("is_default")
   Boolean isDefault;
@@ -65,6 +74,7 @@ private CardholderCreateParams(
       Billing billing,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       Boolean isDefault,
       Map<String, String> metadata,
       String name,
@@ -75,6 +85,7 @@ private CardholderCreateParams(
     this.billing = billing;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.isDefault = isDefault;
     this.metadata = metadata;
     this.name = name;
@@ -96,6 +107,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean isDefault;
 
     private Map<String, String> metadata;
@@ -115,6 +128,7 @@ public CardholderCreateParams build() {
           this.billing,
           this.email,
           this.expand,
+          this.extraParams,
           this.isDefault,
           this.metadata,
           this.name,
@@ -171,6 +185,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardholderCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardholderCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Specifies whether to set this as the default cardholder. */
     public Builder setIsDefault(Boolean isDefault) {
       this.isDefault = isDefault;
@@ -251,6 +291,15 @@ public static class AuthorizationControls {
     @SerializedName("blocked_categories")
     List<BlockedCategory> blockedCategories;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Limit the spending with rules based on time intervals and categories. */
     @SerializedName("spending_limits")
     List<SpendingLimit> spendingLimits;
@@ -258,9 +307,11 @@ public static class AuthorizationControls {
     private AuthorizationControls(
         List<AllowedCategory> allowedCategories,
         List<BlockedCategory> blockedCategories,
+        Map<String, Object> extraParams,
         List<SpendingLimit> spendingLimits) {
       this.allowedCategories = allowedCategories;
       this.blockedCategories = blockedCategories;
+      this.extraParams = extraParams;
       this.spendingLimits = spendingLimits;
     }
 
@@ -273,12 +324,14 @@ public static class Builder {
 
       private List<BlockedCategory> blockedCategories;
 
+      private Map<String, Object> extraParams;
+
       private List<SpendingLimit> spendingLimits;
 
       /** Finalize and obtain parameter instance from this builder. */
       public AuthorizationControls build() {
         return new AuthorizationControls(
-            this.allowedCategories, this.blockedCategories, this.spendingLimits);
+            this.allowedCategories, this.blockedCategories, this.extraParams, this.spendingLimits);
       }
 
       /**
@@ -323,6 +376,33 @@ public Builder addAllBlockedCategory(List<BlockedCategory> elements) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardholderCreateParams.AuthorizationControls#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardholderCreateParams.AuthorizationControls#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Add an element to `spendingLimits` list. A list is initialized for the first `add/addAll`
        * call, and subsequent calls adds additional elements to the original list. See {@link
@@ -377,6 +457,15 @@ public static class SpendingLimit {
       @SerializedName("categories")
       List<Category> categories;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The time interval with which to apply this spending limit towards. Allowed values are
        * 'per_authorization', 'daily', 'weekly', 'monthly', 'yearly', and 'all_time'.
@@ -384,9 +473,14 @@ public static class SpendingLimit {
       @SerializedName("interval")
       Interval interval;
 
-      private SpendingLimit(Long amount, List<Category> categories, Interval interval) {
+      private SpendingLimit(
+          Long amount,
+          List<Category> categories,
+          Map<String, Object> extraParams,
+          Interval interval) {
         this.amount = amount;
         this.categories = categories;
+        this.extraParams = extraParams;
         this.interval = interval;
       }
 
@@ -400,11 +494,13 @@ public static class Builder {
 
         private List<Category> categories;
 
+        private Map<String, Object> extraParams;
+
         private Interval interval;
 
         /** Finalize and obtain parameter instance from this builder. */
         public SpendingLimit build() {
-          return new SpendingLimit(this.amount, this.categories, this.interval);
+          return new SpendingLimit(this.amount, this.categories, this.extraParams, this.interval);
         }
 
         /** Maximum amount allowed to spend per time interval. */
@@ -441,6 +537,34 @@ public Builder addAllCategory(List<Category> elements) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardholderCreateParams.AuthorizationControls.SpendingLimit#extraParams}
+         * for the field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardholderCreateParams.AuthorizationControls.SpendingLimit#extraParams}
+         * for the field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * The time interval with which to apply this spending limit towards. Allowed values are
          * 'per_authorization', 'daily', 'weekly', 'monthly', 'yearly', and 'all_time'.
@@ -3127,11 +3251,21 @@ public static class Billing {
     @SerializedName("address")
     Address address;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("name")
     String name;
 
-    private Billing(Address address, String name) {
+    private Billing(Address address, Map<String, Object> extraParams, String name) {
       this.address = address;
+      this.extraParams = extraParams;
       this.name = name;
     }
 
@@ -3142,11 +3276,13 @@ public static Builder builder() {
     public static class Builder {
       private Address address;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Billing build() {
-        return new Billing(this.address, this.name);
+        return new Billing(this.address, this.extraParams, this.name);
       }
 
       public Builder setAddress(Address address) {
@@ -3154,6 +3290,32 @@ public Builder setAddress(Address address) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardholderCreateParams.Billing#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardholderCreateParams.Billing#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       public Builder setName(String name) {
         this.name = name;
         return this;
@@ -3167,6 +3329,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -3182,12 +3353,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -3203,6 +3376,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -3214,7 +3389,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -3227,6 +3408,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardholderCreateParams.Billing.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardholderCreateParams.Billing.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
diff --git a/src/main/java/com/stripe/param/issuing/CardholderListParams.java b/src/main/java/com/stripe/param/issuing/CardholderListParams.java
index 397562bfdb2..a27fed3d6cc 100644
--- a/src/main/java/com/stripe/param/issuing/CardholderListParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardholderListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class CardholderListParams extends ApiRequestParams {
@@ -30,6 +32,15 @@ public class CardholderListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Only return the default cardholder. */
   @SerializedName("is_default")
   Boolean isDefault;
@@ -69,6 +80,7 @@ private CardholderListParams(
       String email,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Boolean isDefault,
       Long limit,
       String phoneNumber,
@@ -79,6 +91,7 @@ private CardholderListParams(
     this.email = email;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.isDefault = isDefault;
     this.limit = limit;
     this.phoneNumber = phoneNumber;
@@ -100,6 +113,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean isDefault;
 
     private Long limit;
@@ -119,6 +134,7 @@ public CardholderListParams build() {
           this.email,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.isDefault,
           this.limit,
           this.phoneNumber,
@@ -182,6 +198,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardholderListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardholderListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Only return the default cardholder. */
     public Builder setIsDefault(Boolean isDefault) {
       this.isDefault = isDefault;
@@ -233,6 +275,15 @@ public Builder setType(Type type) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -249,7 +300,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -261,6 +313,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -271,7 +325,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardholderListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardholderListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/issuing/CardholderRetrieveParams.java b/src/main/java/com/stripe/param/issuing/CardholderRetrieveParams.java
index fa54ce94e9e..3f1221c184e 100644
--- a/src/main/java/com/stripe/param/issuing/CardholderRetrieveParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardholderRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class CardholderRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private CardholderRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private CardholderRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public CardholderRetrieveParams build() {
-      return new CardholderRetrieveParams(this.expand);
+      return new CardholderRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardholderRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardholderRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/issuing/CardholderUpdateParams.java b/src/main/java/com/stripe/param/issuing/CardholderUpdateParams.java
index 098ba2c26b1..3730ac1ccc0 100644
--- a/src/main/java/com/stripe/param/issuing/CardholderUpdateParams.java
+++ b/src/main/java/com/stripe/param/issuing/CardholderUpdateParams.java
@@ -31,6 +31,15 @@ public class CardholderUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** Specifies whether to set this as the default cardholder. */
   @SerializedName("is_default")
   Boolean isDefault;
@@ -59,6 +68,7 @@ private CardholderUpdateParams(
       Billing billing,
       String email,
       List<String> expand,
+      Map<String, Object> extraParams,
       Boolean isDefault,
       Map<String, String> metadata,
       String phoneNumber,
@@ -67,6 +77,7 @@ private CardholderUpdateParams(
     this.billing = billing;
     this.email = email;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.isDefault = isDefault;
     this.metadata = metadata;
     this.phoneNumber = phoneNumber;
@@ -86,6 +97,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Boolean isDefault;
 
     private Map<String, String> metadata;
@@ -101,6 +114,7 @@ public CardholderUpdateParams build() {
           this.billing,
           this.email,
           this.expand,
+          this.extraParams,
           this.isDefault,
           this.metadata,
           this.phoneNumber,
@@ -155,6 +169,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * CardholderUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link CardholderUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** Specifies whether to set this as the default cardholder. */
     public Builder setIsDefault(Boolean isDefault) {
       this.isDefault = isDefault;
@@ -220,6 +260,15 @@ public static class AuthorizationControls {
     @SerializedName("blocked_categories")
     List<BlockedCategory> blockedCategories;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Limit the spending with rules based on time intervals and categories. */
     @SerializedName("spending_limits")
     List<SpendingLimit> spendingLimits;
@@ -227,9 +276,11 @@ public static class AuthorizationControls {
     private AuthorizationControls(
         List<AllowedCategory> allowedCategories,
         List<BlockedCategory> blockedCategories,
+        Map<String, Object> extraParams,
         List<SpendingLimit> spendingLimits) {
       this.allowedCategories = allowedCategories;
       this.blockedCategories = blockedCategories;
+      this.extraParams = extraParams;
       this.spendingLimits = spendingLimits;
     }
 
@@ -242,12 +293,14 @@ public static class Builder {
 
       private List<BlockedCategory> blockedCategories;
 
+      private Map<String, Object> extraParams;
+
       private List<SpendingLimit> spendingLimits;
 
       /** Finalize and obtain parameter instance from this builder. */
       public AuthorizationControls build() {
         return new AuthorizationControls(
-            this.allowedCategories, this.blockedCategories, this.spendingLimits);
+            this.allowedCategories, this.blockedCategories, this.extraParams, this.spendingLimits);
       }
 
       /**
@@ -292,6 +345,33 @@ public Builder addAllBlockedCategory(List<BlockedCategory> elements) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardholderUpdateParams.AuthorizationControls#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardholderUpdateParams.AuthorizationControls#extraParams} for the field
+       * documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /**
        * Add an element to `spendingLimits` list. A list is initialized for the first `add/addAll`
        * call, and subsequent calls adds additional elements to the original list. See {@link
@@ -346,6 +426,15 @@ public static class SpendingLimit {
       @SerializedName("categories")
       List<Category> categories;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * The time interval with which to apply this spending limit towards. Allowed values are
        * 'per_authorization', 'daily', 'weekly', 'monthly', 'yearly', and 'all_time'.
@@ -353,9 +442,14 @@ public static class SpendingLimit {
       @SerializedName("interval")
       Interval interval;
 
-      private SpendingLimit(Long amount, List<Category> categories, Interval interval) {
+      private SpendingLimit(
+          Long amount,
+          List<Category> categories,
+          Map<String, Object> extraParams,
+          Interval interval) {
         this.amount = amount;
         this.categories = categories;
+        this.extraParams = extraParams;
         this.interval = interval;
       }
 
@@ -369,11 +463,13 @@ public static class Builder {
 
         private List<Category> categories;
 
+        private Map<String, Object> extraParams;
+
         private Interval interval;
 
         /** Finalize and obtain parameter instance from this builder. */
         public SpendingLimit build() {
-          return new SpendingLimit(this.amount, this.categories, this.interval);
+          return new SpendingLimit(this.amount, this.categories, this.extraParams, this.interval);
         }
 
         /** Maximum amount allowed to spend per time interval. */
@@ -410,6 +506,34 @@ public Builder addAllCategory(List<Category> elements) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardholderUpdateParams.AuthorizationControls.SpendingLimit#extraParams}
+         * for the field documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardholderUpdateParams.AuthorizationControls.SpendingLimit#extraParams}
+         * for the field documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * The time interval with which to apply this spending limit towards. Allowed values are
          * 'per_authorization', 'daily', 'weekly', 'monthly', 'yearly', and 'all_time'.
@@ -3096,11 +3220,21 @@ public static class Billing {
     @SerializedName("address")
     Address address;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("name")
     String name;
 
-    private Billing(Address address, String name) {
+    private Billing(Address address, Map<String, Object> extraParams, String name) {
       this.address = address;
+      this.extraParams = extraParams;
       this.name = name;
     }
 
@@ -3111,11 +3245,13 @@ public static Builder builder() {
     public static class Builder {
       private Address address;
 
+      private Map<String, Object> extraParams;
+
       private String name;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Billing build() {
-        return new Billing(this.address, this.name);
+        return new Billing(this.address, this.extraParams, this.name);
       }
 
       public Builder setAddress(Address address) {
@@ -3123,6 +3259,32 @@ public Builder setAddress(Address address) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * CardholderUpdateParams.Billing#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link CardholderUpdateParams.Billing#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       public Builder setName(String name) {
         this.name = name;
         return this;
@@ -3136,6 +3298,15 @@ public static class Address {
       @SerializedName("country")
       String country;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       @SerializedName("line1")
       String line1;
 
@@ -3151,12 +3322,14 @@ public static class Address {
       private Address(
           String city,
           String country,
+          Map<String, Object> extraParams,
           String line1,
           String line2,
           String postalCode,
           String state) {
         this.city = city;
         this.country = country;
+        this.extraParams = extraParams;
         this.line1 = line1;
         this.line2 = line2;
         this.postalCode = postalCode;
@@ -3172,6 +3345,8 @@ public static class Builder {
 
         private String country;
 
+        private Map<String, Object> extraParams;
+
         private String line1;
 
         private String line2;
@@ -3183,7 +3358,13 @@ public static class Builder {
         /** Finalize and obtain parameter instance from this builder. */
         public Address build() {
           return new Address(
-              this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+              this.city,
+              this.country,
+              this.extraParams,
+              this.line1,
+              this.line2,
+              this.postalCode,
+              this.state);
         }
 
         public Builder setCity(String city) {
@@ -3196,6 +3377,34 @@ public Builder setCountry(String country) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardholderUpdateParams.Billing.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link CardholderUpdateParams.Billing.Address#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         public Builder setLine1(String line1) {
           this.line1 = line1;
           return this;
diff --git a/src/main/java/com/stripe/param/issuing/DisputeCreateParams.java b/src/main/java/com/stripe/param/issuing/DisputeCreateParams.java
index 98088bc6aef..9bedcc37306 100644
--- a/src/main/java/com/stripe/param/issuing/DisputeCreateParams.java
+++ b/src/main/java/com/stripe/param/issuing/DisputeCreateParams.java
@@ -32,6 +32,15 @@ public class DisputeCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -49,12 +58,14 @@ private DisputeCreateParams(
       String disputedTransaction,
       Evidence evidence,
       List<String> expand,
+      Map<String, Object> extraParams,
       Map<String, String> metadata,
       Reason reason) {
     this.amount = amount;
     this.disputedTransaction = disputedTransaction;
     this.evidence = evidence;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.reason = reason;
   }
@@ -72,6 +83,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private Reason reason;
@@ -83,6 +96,7 @@ public DisputeCreateParams build() {
           this.disputedTransaction,
           this.evidence,
           this.expand,
+          this.extraParams,
           this.metadata,
           this.reason);
     }
@@ -136,6 +150,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * DisputeCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link DisputeCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
@@ -170,6 +210,15 @@ public Builder setReason(Reason reason) {
   }
 
   public static class Evidence {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /**
      * Evidence to support a fraudulent dispute. Only provide this if your dispute's `reason` is
      * `fraudulent`.
@@ -184,7 +233,8 @@ public static class Evidence {
     @SerializedName("other")
     Other other;
 
-    private Evidence(Fraudulent fraudulent, Other other) {
+    private Evidence(Map<String, Object> extraParams, Fraudulent fraudulent, Other other) {
+      this.extraParams = extraParams;
       this.fraudulent = fraudulent;
       this.other = other;
     }
@@ -194,13 +244,41 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Fraudulent fraudulent;
 
       private Other other;
 
       /** Finalize and obtain parameter instance from this builder. */
       public Evidence build() {
-        return new Evidence(this.fraudulent, this.other);
+        return new Evidence(this.extraParams, this.fraudulent, this.other);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * DisputeCreateParams.Evidence#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link DisputeCreateParams.Evidence#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /**
@@ -227,6 +305,15 @@ public static class Fraudulent {
       @SerializedName("dispute_explanation")
       String disputeExplanation;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * (ID of a [file upload](https://stripe.com/docs/guides/file-upload)) Additional file
        * evidence supporting your dispute.
@@ -234,8 +321,10 @@ public static class Fraudulent {
       @SerializedName("uncategorized_file")
       String uncategorizedFile;
 
-      private Fraudulent(String disputeExplanation, String uncategorizedFile) {
+      private Fraudulent(
+          String disputeExplanation, Map<String, Object> extraParams, String uncategorizedFile) {
         this.disputeExplanation = disputeExplanation;
+        this.extraParams = extraParams;
         this.uncategorizedFile = uncategorizedFile;
       }
 
@@ -246,11 +335,13 @@ public static Builder builder() {
       public static class Builder {
         private String disputeExplanation;
 
+        private Map<String, Object> extraParams;
+
         private String uncategorizedFile;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Fraudulent build() {
-          return new Fraudulent(this.disputeExplanation, this.uncategorizedFile);
+          return new Fraudulent(this.disputeExplanation, this.extraParams, this.uncategorizedFile);
         }
 
         /** Brief freeform text explaining why you are disputing this transaction. */
@@ -259,6 +350,34 @@ public Builder setDisputeExplanation(String disputeExplanation) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link DisputeCreateParams.Evidence.Fraudulent#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link DisputeCreateParams.Evidence.Fraudulent#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * (ID of a [file upload](https://stripe.com/docs/guides/file-upload)) Additional file
          * evidence supporting your dispute.
@@ -275,6 +394,15 @@ public static class Other {
       @SerializedName("dispute_explanation")
       String disputeExplanation;
 
+      /**
+       * Map of extra parameters for custom features not available in this client library. The
+       * content in this map is not serialized under this field's {@code @SerializedName} value.
+       * Instead, each key/value pair is serialized as if the key is a root-level field (serialized)
+       * name in this param object. Effectively, this map is flattened to its parent instance.
+       */
+      @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+      Map<String, Object> extraParams;
+
       /**
        * (ID of a [file upload](https://stripe.com/docs/guides/file-upload)) Additional file
        * evidence supporting your dispute.
@@ -282,8 +410,10 @@ public static class Other {
       @SerializedName("uncategorized_file")
       String uncategorizedFile;
 
-      private Other(String disputeExplanation, String uncategorizedFile) {
+      private Other(
+          String disputeExplanation, Map<String, Object> extraParams, String uncategorizedFile) {
         this.disputeExplanation = disputeExplanation;
+        this.extraParams = extraParams;
         this.uncategorizedFile = uncategorizedFile;
       }
 
@@ -294,11 +424,13 @@ public static Builder builder() {
       public static class Builder {
         private String disputeExplanation;
 
+        private Map<String, Object> extraParams;
+
         private String uncategorizedFile;
 
         /** Finalize and obtain parameter instance from this builder. */
         public Other build() {
-          return new Other(this.disputeExplanation, this.uncategorizedFile);
+          return new Other(this.disputeExplanation, this.extraParams, this.uncategorizedFile);
         }
 
         /** Brief freeform text explaining why you are disputing this transaction. */
@@ -307,6 +439,34 @@ public Builder setDisputeExplanation(String disputeExplanation) {
           return this;
         }
 
+        /**
+         * Add a key/value pair to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link DisputeCreateParams.Evidence.Other#extraParams} for the field
+         * documentation.
+         */
+        public Builder putExtraParam(String key, Object value) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.put(key, value);
+          return this;
+        }
+
+        /**
+         * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+         * `put/putAll` call, and subsequent calls add additional key/value pairs to the original
+         * map. See {@link DisputeCreateParams.Evidence.Other#extraParams} for the field
+         * documentation.
+         */
+        public Builder putAllExtraParam(Map<String, Object> map) {
+          if (this.extraParams == null) {
+            this.extraParams = new HashMap<>();
+          }
+          this.extraParams.putAll(map);
+          return this;
+        }
+
         /**
          * (ID of a [file upload](https://stripe.com/docs/guides/file-upload)) Additional file
          * evidence supporting your dispute.
diff --git a/src/main/java/com/stripe/param/issuing/DisputeListParams.java b/src/main/java/com/stripe/param/issuing/DisputeListParams.java
index d6d06a502e6..46bbc0cad10 100644
--- a/src/main/java/com/stripe/param/issuing/DisputeListParams.java
+++ b/src/main/java/com/stripe/param/issuing/DisputeListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class DisputeListParams extends ApiRequestParams {
   /** Only return issuing disputes that were created during the given date interval. */
@@ -29,6 +31,15 @@ public class DisputeListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -50,12 +61,14 @@ private DisputeListParams(
       String disputedTransaction,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter) {
     this.created = created;
     this.disputedTransaction = disputedTransaction;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -73,6 +86,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -84,6 +99,7 @@ public DisputeListParams build() {
           this.disputedTransaction,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter);
     }
@@ -143,6 +159,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * DisputeListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link DisputeListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -165,6 +207,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -181,7 +232,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -193,6 +245,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -203,7 +257,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * DisputeListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link DisputeListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/issuing/DisputeRetrieveParams.java b/src/main/java/com/stripe/param/issuing/DisputeRetrieveParams.java
index d809055f8b3..d6fbe78121a 100644
--- a/src/main/java/com/stripe/param/issuing/DisputeRetrieveParams.java
+++ b/src/main/java/com/stripe/param/issuing/DisputeRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class DisputeRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private DisputeRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private DisputeRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public DisputeRetrieveParams build() {
-      return new DisputeRetrieveParams(this.expand);
+      return new DisputeRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * DisputeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link DisputeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/issuing/DisputeUpdateParams.java b/src/main/java/com/stripe/param/issuing/DisputeUpdateParams.java
index 74c9c948e71..955833628a8 100644
--- a/src/main/java/com/stripe/param/issuing/DisputeUpdateParams.java
+++ b/src/main/java/com/stripe/param/issuing/DisputeUpdateParams.java
@@ -14,6 +14,15 @@ public class DisputeUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -22,8 +31,10 @@ public class DisputeUpdateParams extends ApiRequestParams {
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private DisputeUpdateParams(List<String> expand, Map<String, String> metadata) {
+  private DisputeUpdateParams(
+      List<String> expand, Map<String, Object> extraParams, Map<String, String> metadata) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -34,11 +45,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public DisputeUpdateParams build() {
-      return new DisputeUpdateParams(this.expand, this.metadata);
+      return new DisputeUpdateParams(this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -67,6 +80,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * DisputeUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link DisputeUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/issuing/TransactionListParams.java b/src/main/java/com/stripe/param/issuing/TransactionListParams.java
index dffa5068976..6a76fe66163 100644
--- a/src/main/java/com/stripe/param/issuing/TransactionListParams.java
+++ b/src/main/java/com/stripe/param/issuing/TransactionListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TransactionListParams extends ApiRequestParams {
   /** Only return issuing transactions that belong to the given card. */
@@ -37,6 +39,15 @@ public class TransactionListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -60,6 +71,7 @@ private TransactionListParams(
       String dispute,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter) {
     this.card = card;
@@ -68,6 +80,7 @@ private TransactionListParams(
     this.dispute = dispute;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -89,6 +102,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -102,6 +117,7 @@ public TransactionListParams build() {
           this.dispute,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter);
     }
@@ -173,6 +189,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransactionListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransactionListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -195,6 +237,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -211,7 +262,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -223,6 +275,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -233,7 +287,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * TransactionListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link TransactionListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/issuing/TransactionRetrieveParams.java b/src/main/java/com/stripe/param/issuing/TransactionRetrieveParams.java
index 44165cbddaa..8ac1be58c46 100644
--- a/src/main/java/com/stripe/param/issuing/TransactionRetrieveParams.java
+++ b/src/main/java/com/stripe/param/issuing/TransactionRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class TransactionRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private TransactionRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private TransactionRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public TransactionRetrieveParams build() {
-      return new TransactionRetrieveParams(this.expand);
+      return new TransactionRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransactionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransactionRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/issuing/TransactionUpdateParams.java b/src/main/java/com/stripe/param/issuing/TransactionUpdateParams.java
index 8458804d476..8d86848fd8d 100644
--- a/src/main/java/com/stripe/param/issuing/TransactionUpdateParams.java
+++ b/src/main/java/com/stripe/param/issuing/TransactionUpdateParams.java
@@ -14,11 +14,22 @@ public class TransactionUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   @SerializedName("metadata")
   Map<String, String> metadata;
 
-  private TransactionUpdateParams(List<String> expand, Map<String, String> metadata) {
+  private TransactionUpdateParams(
+      List<String> expand, Map<String, Object> extraParams, Map<String, String> metadata) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
   }
 
@@ -29,11 +40,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     /** Finalize and obtain parameter instance from this builder. */
     public TransactionUpdateParams build() {
-      return new TransactionUpdateParams(this.expand, this.metadata);
+      return new TransactionUpdateParams(this.expand, this.extraParams, this.metadata);
     }
 
     /**
@@ -62,6 +75,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * TransactionUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link TransactionUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/radar/ValueListCreateParams.java b/src/main/java/com/stripe/param/radar/ValueListCreateParams.java
index eed9b81825b..4bdc44d3f92 100644
--- a/src/main/java/com/stripe/param/radar/ValueListCreateParams.java
+++ b/src/main/java/com/stripe/param/radar/ValueListCreateParams.java
@@ -19,6 +19,15 @@ public class ValueListCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Type of the items in the value list. One of `card_fingerprint`, `card_bin`, `email`,
    * `ip_address`, `country`, `string`, or `case_sensitive_string`. Use `string` if the item type is
@@ -42,11 +51,13 @@ public class ValueListCreateParams extends ApiRequestParams {
   private ValueListCreateParams(
       String alias,
       List<String> expand,
+      Map<String, Object> extraParams,
       ItemType itemType,
       Map<String, String> metadata,
       String name) {
     this.alias = alias;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.itemType = itemType;
     this.metadata = metadata;
     this.name = name;
@@ -61,6 +72,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private ItemType itemType;
 
     private Map<String, String> metadata;
@@ -70,7 +83,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public ValueListCreateParams build() {
       return new ValueListCreateParams(
-          this.alias, this.expand, this.itemType, this.metadata, this.name);
+          this.alias, this.expand, this.extraParams, this.itemType, this.metadata, this.name);
     }
 
     /** The name of the value list for use in rules. */
@@ -105,6 +118,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ValueListCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ValueListCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Type of the items in the value list. One of `card_fingerprint`, `card_bin`, `email`,
      * `ip_address`, `country`, `string`, or `case_sensitive_string`. Use `string` if the item type
diff --git a/src/main/java/com/stripe/param/radar/ValueListItemCreateParams.java b/src/main/java/com/stripe/param/radar/ValueListItemCreateParams.java
index cba2a30bfc1..5a45b039f42 100644
--- a/src/main/java/com/stripe/param/radar/ValueListItemCreateParams.java
+++ b/src/main/java/com/stripe/param/radar/ValueListItemCreateParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ValueListItemCreateParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The value of the item (whose type must match the type of the parent value list). */
   @SerializedName("value")
   String value;
@@ -20,8 +31,10 @@ public class ValueListItemCreateParams extends ApiRequestParams {
   @SerializedName("value_list")
   String valueList;
 
-  private ValueListItemCreateParams(List<String> expand, String value, String valueList) {
+  private ValueListItemCreateParams(
+      List<String> expand, Map<String, Object> extraParams, String value, String valueList) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.value = value;
     this.valueList = valueList;
   }
@@ -33,13 +46,16 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String value;
 
     private String valueList;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ValueListItemCreateParams build() {
-      return new ValueListItemCreateParams(this.expand, this.value, this.valueList);
+      return new ValueListItemCreateParams(
+          this.expand, this.extraParams, this.value, this.valueList);
     }
 
     /**
@@ -68,6 +84,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ValueListItemCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ValueListItemCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The value of the item (whose type must match the type of the parent value list). */
     public Builder setValue(String value) {
       this.value = value;
diff --git a/src/main/java/com/stripe/param/radar/ValueListItemListParams.java b/src/main/java/com/stripe/param/radar/ValueListItemListParams.java
index 4b708104808..26b4e180744 100644
--- a/src/main/java/com/stripe/param/radar/ValueListItemListParams.java
+++ b/src/main/java/com/stripe/param/radar/ValueListItemListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ValueListItemListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -24,6 +26,15 @@ public class ValueListItemListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -55,6 +66,7 @@ private ValueListItemListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter,
       String value,
@@ -62,6 +74,7 @@ private ValueListItemListParams(
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
     this.value = value;
@@ -79,6 +92,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -93,6 +108,7 @@ public ValueListItemListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter,
           this.value,
@@ -146,6 +162,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ValueListItemListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ValueListItemListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -183,6 +225,15 @@ public Builder setValueList(String valueList) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -199,7 +250,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -211,6 +263,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -221,7 +275,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ValueListItemListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ValueListItemListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/radar/ValueListItemRetrieveParams.java b/src/main/java/com/stripe/param/radar/ValueListItemRetrieveParams.java
index 0760f8fd1e1..b852a3741e4 100644
--- a/src/main/java/com/stripe/param/radar/ValueListItemRetrieveParams.java
+++ b/src/main/java/com/stripe/param/radar/ValueListItemRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ValueListItemRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ValueListItemRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ValueListItemRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ValueListItemRetrieveParams build() {
-      return new ValueListItemRetrieveParams(this.expand);
+      return new ValueListItemRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ValueListItemRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ValueListItemRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/radar/ValueListListParams.java b/src/main/java/com/stripe/param/radar/ValueListListParams.java
index aa03c974aee..dae6c307b7f 100644
--- a/src/main/java/com/stripe/param/radar/ValueListListParams.java
+++ b/src/main/java/com/stripe/param/radar/ValueListListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ValueListListParams extends ApiRequestParams {
   /** The alias used to reference the value list when writing rules. */
@@ -32,6 +34,15 @@ public class ValueListListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -54,6 +65,7 @@ private ValueListListParams(
       Object created,
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String startingAfter) {
     this.alias = alias;
@@ -61,6 +73,7 @@ private ValueListListParams(
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -80,6 +93,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -92,6 +107,7 @@ public ValueListListParams build() {
           this.created,
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.startingAfter);
     }
@@ -155,6 +171,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ValueListListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ValueListListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -177,6 +219,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -193,7 +244,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -205,6 +257,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -215,7 +269,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ValueListListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ValueListListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/radar/ValueListRetrieveParams.java b/src/main/java/com/stripe/param/radar/ValueListRetrieveParams.java
index 59e0246fdbd..116780f0275 100644
--- a/src/main/java/com/stripe/param/radar/ValueListRetrieveParams.java
+++ b/src/main/java/com/stripe/param/radar/ValueListRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ValueListRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ValueListRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ValueListRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ValueListRetrieveParams build() {
-      return new ValueListRetrieveParams(this.expand);
+      return new ValueListRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ValueListRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ValueListRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/radar/ValueListUpdateParams.java b/src/main/java/com/stripe/param/radar/ValueListUpdateParams.java
index 3a584f0045d..f57b2bcef52 100644
--- a/src/main/java/com/stripe/param/radar/ValueListUpdateParams.java
+++ b/src/main/java/com/stripe/param/radar/ValueListUpdateParams.java
@@ -18,6 +18,15 @@ public class ValueListUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Set of key-value pairs that you can attach to an object. This can be useful for storing
    * additional information about the object in a structured format. Individual keys can be unset by
@@ -31,9 +40,14 @@ public class ValueListUpdateParams extends ApiRequestParams {
   String name;
 
   private ValueListUpdateParams(
-      String alias, List<String> expand, Map<String, String> metadata, String name) {
+      String alias,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Map<String, String> metadata,
+      String name) {
     this.alias = alias;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.metadata = metadata;
     this.name = name;
   }
@@ -47,13 +61,16 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Map<String, String> metadata;
 
     private String name;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ValueListUpdateParams build() {
-      return new ValueListUpdateParams(this.alias, this.expand, this.metadata, this.name);
+      return new ValueListUpdateParams(
+          this.alias, this.expand, this.extraParams, this.metadata, this.name);
     }
 
     /** The name of the value list for use in rules. */
@@ -88,6 +105,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ValueListUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ValueListUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Add a key/value pair to `metadata` map. A map is initialized for the first `put/putAll` call,
      * and subsequent calls add additional key/value pairs to the original map. See {@link
diff --git a/src/main/java/com/stripe/param/reporting/ReportRunCreateParams.java b/src/main/java/com/stripe/param/reporting/ReportRunCreateParams.java
index 700642b3c26..407666cada1 100644
--- a/src/main/java/com/stripe/param/reporting/ReportRunCreateParams.java
+++ b/src/main/java/com/stripe/param/reporting/ReportRunCreateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import lombok.Getter;
 
 public class ReportRunCreateParams extends ApiRequestParams {
@@ -13,6 +15,15 @@ public class ReportRunCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Parameters specifying how the report should be run. Different Report Types have different
    * required and optional parameters, listed in the [API Access to
@@ -28,8 +39,13 @@ public class ReportRunCreateParams extends ApiRequestParams {
   @SerializedName("report_type")
   String reportType;
 
-  private ReportRunCreateParams(List<String> expand, Parameters parameters, String reportType) {
+  private ReportRunCreateParams(
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Parameters parameters,
+      String reportType) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.parameters = parameters;
     this.reportType = reportType;
   }
@@ -41,13 +57,16 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Parameters parameters;
 
     private String reportType;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ReportRunCreateParams build() {
-      return new ReportRunCreateParams(this.expand, this.parameters, this.reportType);
+      return new ReportRunCreateParams(
+          this.expand, this.extraParams, this.parameters, this.reportType);
     }
 
     /**
@@ -76,6 +95,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReportRunCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReportRunCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Parameters specifying how the report should be run. Different Report Types have different
      * required and optional parameters, listed in the [API Access to
@@ -112,6 +157,15 @@ public static class Parameters {
     @SerializedName("currency")
     String currency;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Ending timestamp of data to be included in the report run (exclusive). */
     @SerializedName("interval_end")
     Long intervalEnd;
@@ -132,6 +186,7 @@ private Parameters(
         List<String> columns,
         String connectedAccount,
         String currency,
+        Map<String, Object> extraParams,
         Long intervalEnd,
         Long intervalStart,
         String payout,
@@ -139,6 +194,7 @@ private Parameters(
       this.columns = columns;
       this.connectedAccount = connectedAccount;
       this.currency = currency;
+      this.extraParams = extraParams;
       this.intervalEnd = intervalEnd;
       this.intervalStart = intervalStart;
       this.payout = payout;
@@ -156,6 +212,8 @@ public static class Builder {
 
       private String currency;
 
+      private Map<String, Object> extraParams;
+
       private Long intervalEnd;
 
       private Long intervalStart;
@@ -170,6 +228,7 @@ public Parameters build() {
             this.columns,
             this.connectedAccount,
             this.currency,
+            this.extraParams,
             this.intervalEnd,
             this.intervalStart,
             this.payout,
@@ -214,6 +273,32 @@ public Builder setCurrency(String currency) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ReportRunCreateParams.Parameters#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ReportRunCreateParams.Parameters#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       /** Ending timestamp of data to be included in the report run (exclusive). */
       public Builder setIntervalEnd(Long intervalEnd) {
         this.intervalEnd = intervalEnd;
diff --git a/src/main/java/com/stripe/param/reporting/ReportRunListParams.java b/src/main/java/com/stripe/param/reporting/ReportRunListParams.java
index a3f070ac89c..37cf8bd3619 100644
--- a/src/main/java/com/stripe/param/reporting/ReportRunListParams.java
+++ b/src/main/java/com/stripe/param/reporting/ReportRunListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReportRunListParams extends ApiRequestParams {
   @SerializedName("created")
@@ -24,6 +26,15 @@ public class ReportRunListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -41,10 +52,16 @@ public class ReportRunListParams extends ApiRequestParams {
   String startingAfter;
 
   private ReportRunListParams(
-      Object created, String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      Object created,
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.created = created;
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -60,6 +77,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -67,7 +86,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public ReportRunListParams build() {
       return new ReportRunListParams(
-          this.created, this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.created,
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.startingAfter);
     }
 
     public Builder setCreated(Created created) {
@@ -117,6 +141,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReportRunListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReportRunListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
@@ -139,6 +189,15 @@ public Builder setStartingAfter(String startingAfter) {
   }
 
   public static class Created {
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     /** Minimum value to filter by (exclusive). */
     @SerializedName("gt")
     Long gt;
@@ -155,7 +214,8 @@ public static class Created {
     @SerializedName("lte")
     Long lte;
 
-    private Created(Long gt, Long gte, Long lt, Long lte) {
+    private Created(Map<String, Object> extraParams, Long gt, Long gte, Long lt, Long lte) {
+      this.extraParams = extraParams;
       this.gt = gt;
       this.gte = gte;
       this.lt = lt;
@@ -167,6 +227,8 @@ public static Builder builder() {
     }
 
     public static class Builder {
+      private Map<String, Object> extraParams;
+
       private Long gt;
 
       private Long gte;
@@ -177,7 +239,33 @@ public static class Builder {
 
       /** Finalize and obtain parameter instance from this builder. */
       public Created build() {
-        return new Created(this.gt, this.gte, this.lt, this.lte);
+        return new Created(this.extraParams, this.gt, this.gte, this.lt, this.lte);
+      }
+
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * ReportRunListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link ReportRunListParams.Created#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
       }
 
       /** Minimum value to filter by (exclusive). */
diff --git a/src/main/java/com/stripe/param/reporting/ReportRunRetrieveParams.java b/src/main/java/com/stripe/param/reporting/ReportRunRetrieveParams.java
index 71c2ac32604..9115306c269 100644
--- a/src/main/java/com/stripe/param/reporting/ReportRunRetrieveParams.java
+++ b/src/main/java/com/stripe/param/reporting/ReportRunRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReportRunRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ReportRunRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ReportRunRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ReportRunRetrieveParams build() {
-      return new ReportRunRetrieveParams(this.expand);
+      return new ReportRunRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReportRunRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReportRunRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/reporting/ReportTypeListParams.java b/src/main/java/com/stripe/param/reporting/ReportTypeListParams.java
index be4a079aa35..fcfd7df40ab 100644
--- a/src/main/java/com/stripe/param/reporting/ReportTypeListParams.java
+++ b/src/main/java/com/stripe/param/reporting/ReportTypeListParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReportTypeListParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ReportTypeListParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ReportTypeListParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ReportTypeListParams build() {
-      return new ReportTypeListParams(this.expand);
+      return new ReportTypeListParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReportTypeListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReportTypeListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/reporting/ReportTypeRetrieveParams.java b/src/main/java/com/stripe/param/reporting/ReportTypeRetrieveParams.java
index 4d41e03d8fd..24e2a734639 100644
--- a/src/main/java/com/stripe/param/reporting/ReportTypeRetrieveParams.java
+++ b/src/main/java/com/stripe/param/reporting/ReportTypeRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReportTypeRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ReportTypeRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ReportTypeRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ReportTypeRetrieveParams build() {
-      return new ReportTypeRetrieveParams(this.expand);
+      return new ReportTypeRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReportTypeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReportTypeRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/sigma/ScheduledQueryRunListParams.java b/src/main/java/com/stripe/param/sigma/ScheduledQueryRunListParams.java
index 7ac78d675d6..a5fd13fad48 100644
--- a/src/main/java/com/stripe/param/sigma/ScheduledQueryRunListParams.java
+++ b/src/main/java/com/stripe/param/sigma/ScheduledQueryRunListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ScheduledQueryRunListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class ScheduledQueryRunListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -38,9 +49,14 @@ public class ScheduledQueryRunListParams extends ApiRequestParams {
   String startingAfter;
 
   private ScheduledQueryRunListParams(
-      String endingBefore, List<String> expand, Long limit, String startingAfter) {
+      String endingBefore,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      Long limit,
+      String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.startingAfter = startingAfter;
   }
@@ -54,6 +70,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String startingAfter;
@@ -61,7 +79,7 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public ScheduledQueryRunListParams build() {
       return new ScheduledQueryRunListParams(
-          this.endingBefore, this.expand, this.limit, this.startingAfter);
+          this.endingBefore, this.expand, this.extraParams, this.limit, this.startingAfter);
     }
 
     /**
@@ -101,6 +119,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ScheduledQueryRunListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ScheduledQueryRunListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/sigma/ScheduledQueryRunRetrieveParams.java b/src/main/java/com/stripe/param/sigma/ScheduledQueryRunRetrieveParams.java
index f826067d09c..f51f03b3e4a 100644
--- a/src/main/java/com/stripe/param/sigma/ScheduledQueryRunRetrieveParams.java
+++ b/src/main/java/com/stripe/param/sigma/ScheduledQueryRunRetrieveParams.java
@@ -5,15 +5,27 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ScheduledQueryRunRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
-  private ScheduledQueryRunRetrieveParams(List<String> expand) {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
+  private ScheduledQueryRunRetrieveParams(List<String> expand, Map<String, Object> extraParams) {
     this.expand = expand;
+    this.extraParams = extraParams;
   }
 
   public static Builder builder() {
@@ -23,9 +35,11 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     /** Finalize and obtain parameter instance from this builder. */
     public ScheduledQueryRunRetrieveParams build() {
-      return new ScheduledQueryRunRetrieveParams(this.expand);
+      return new ScheduledQueryRunRetrieveParams(this.expand, this.extraParams);
     }
 
     /**
@@ -53,5 +67,31 @@ public Builder addAllExpand(List<String> elements) {
       this.expand.addAll(elements);
       return this;
     }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ScheduledQueryRunRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ScheduledQueryRunRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
   }
 }
diff --git a/src/main/java/com/stripe/param/terminal/ConnectionTokenCreateParams.java b/src/main/java/com/stripe/param/terminal/ConnectionTokenCreateParams.java
index 6ff44a9505a..fc53d792293 100644
--- a/src/main/java/com/stripe/param/terminal/ConnectionTokenCreateParams.java
+++ b/src/main/java/com/stripe/param/terminal/ConnectionTokenCreateParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ConnectionTokenCreateParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * To [group
    * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -20,8 +31,10 @@ public class ConnectionTokenCreateParams extends ApiRequestParams {
   @SerializedName("operator_account")
   String operatorAccount;
 
-  private ConnectionTokenCreateParams(List<String> expand, String operatorAccount) {
+  private ConnectionTokenCreateParams(
+      List<String> expand, Map<String, Object> extraParams, String operatorAccount) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.operatorAccount = operatorAccount;
   }
 
@@ -32,11 +45,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String operatorAccount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ConnectionTokenCreateParams build() {
-      return new ConnectionTokenCreateParams(this.expand, this.operatorAccount);
+      return new ConnectionTokenCreateParams(this.expand, this.extraParams, this.operatorAccount);
     }
 
     /**
@@ -65,6 +80,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ConnectionTokenCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ConnectionTokenCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * To [group
      * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
diff --git a/src/main/java/com/stripe/param/terminal/LocationCreateParams.java b/src/main/java/com/stripe/param/terminal/LocationCreateParams.java
index 57160d5a596..0c351999a1b 100644
--- a/src/main/java/com/stripe/param/terminal/LocationCreateParams.java
+++ b/src/main/java/com/stripe/param/terminal/LocationCreateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class LocationCreateParams extends ApiRequestParams {
   /** The full address of the location. */
@@ -20,6 +22,15 @@ public class LocationCreateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * To [group
    * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -29,10 +40,15 @@ public class LocationCreateParams extends ApiRequestParams {
   String operatorAccount;
 
   private LocationCreateParams(
-      Address address, String displayName, List<String> expand, String operatorAccount) {
+      Address address,
+      String displayName,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      String operatorAccount) {
     this.address = address;
     this.displayName = displayName;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.operatorAccount = operatorAccount;
   }
 
@@ -47,12 +63,14 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String operatorAccount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public LocationCreateParams build() {
       return new LocationCreateParams(
-          this.address, this.displayName, this.expand, this.operatorAccount);
+          this.address, this.displayName, this.expand, this.extraParams, this.operatorAccount);
     }
 
     /** The full address of the location. */
@@ -93,6 +111,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * LocationCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link LocationCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * To [group
      * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -112,6 +156,15 @@ public static class Address {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("line1")
     String line1;
 
@@ -125,9 +178,16 @@ public static class Address {
     String state;
 
     private Address(
-        String city, String country, String line1, String line2, String postalCode, String state) {
+        String city,
+        String country,
+        Map<String, Object> extraParams,
+        String line1,
+        String line2,
+        String postalCode,
+        String state) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -143,6 +203,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -154,7 +216,13 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Address build() {
         return new Address(
-            this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+            this.city,
+            this.country,
+            this.extraParams,
+            this.line1,
+            this.line2,
+            this.postalCode,
+            this.state);
       }
 
       public Builder setCity(String city) {
@@ -167,6 +235,32 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * LocationCreateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link LocationCreateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       public Builder setLine1(String line1) {
         this.line1 = line1;
         return this;
diff --git a/src/main/java/com/stripe/param/terminal/LocationDeleteParams.java b/src/main/java/com/stripe/param/terminal/LocationDeleteParams.java
index 61c32a1fc70..dbf6c99e7d7 100644
--- a/src/main/java/com/stripe/param/terminal/LocationDeleteParams.java
+++ b/src/main/java/com/stripe/param/terminal/LocationDeleteParams.java
@@ -4,8 +4,19 @@
 
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
+import java.util.HashMap;
+import java.util.Map;
 
 public class LocationDeleteParams extends ApiRequestParams {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * To [group
    * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -14,7 +25,8 @@ public class LocationDeleteParams extends ApiRequestParams {
   @SerializedName("operator_account")
   String operatorAccount;
 
-  private LocationDeleteParams(String operatorAccount) {
+  private LocationDeleteParams(Map<String, Object> extraParams, String operatorAccount) {
+    this.extraParams = extraParams;
     this.operatorAccount = operatorAccount;
   }
 
@@ -23,11 +35,39 @@ public static Builder builder() {
   }
 
   public static class Builder {
+    private Map<String, Object> extraParams;
+
     private String operatorAccount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public LocationDeleteParams build() {
-      return new LocationDeleteParams(this.operatorAccount);
+      return new LocationDeleteParams(this.extraParams, this.operatorAccount);
+    }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * LocationDeleteParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link LocationDeleteParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
     }
 
     /**
diff --git a/src/main/java/com/stripe/param/terminal/LocationListParams.java b/src/main/java/com/stripe/param/terminal/LocationListParams.java
index 1a9573ad40a..4182f353703 100644
--- a/src/main/java/com/stripe/param/terminal/LocationListParams.java
+++ b/src/main/java/com/stripe/param/terminal/LocationListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class LocationListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class LocationListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -48,11 +59,13 @@ public class LocationListParams extends ApiRequestParams {
   private LocationListParams(
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String operatorAccount,
       String startingAfter) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.operatorAccount = operatorAccount;
     this.startingAfter = startingAfter;
@@ -67,6 +80,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String operatorAccount;
@@ -76,7 +91,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public LocationListParams build() {
       return new LocationListParams(
-          this.endingBefore, this.expand, this.limit, this.operatorAccount, this.startingAfter);
+          this.endingBefore,
+          this.expand,
+          this.extraParams,
+          this.limit,
+          this.operatorAccount,
+          this.startingAfter);
     }
 
     /**
@@ -116,6 +136,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * LocationListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link LocationListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/terminal/LocationRetrieveParams.java b/src/main/java/com/stripe/param/terminal/LocationRetrieveParams.java
index 61ae8422f83..93802ff2b38 100644
--- a/src/main/java/com/stripe/param/terminal/LocationRetrieveParams.java
+++ b/src/main/java/com/stripe/param/terminal/LocationRetrieveParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class LocationRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * To [group
    * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -20,8 +31,10 @@ public class LocationRetrieveParams extends ApiRequestParams {
   @SerializedName("operator_account")
   String operatorAccount;
 
-  private LocationRetrieveParams(List<String> expand, String operatorAccount) {
+  private LocationRetrieveParams(
+      List<String> expand, Map<String, Object> extraParams, String operatorAccount) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.operatorAccount = operatorAccount;
   }
 
@@ -32,11 +45,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String operatorAccount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public LocationRetrieveParams build() {
-      return new LocationRetrieveParams(this.expand, this.operatorAccount);
+      return new LocationRetrieveParams(this.expand, this.extraParams, this.operatorAccount);
     }
 
     /**
@@ -65,6 +80,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * LocationRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link LocationRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * To [group
      * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
diff --git a/src/main/java/com/stripe/param/terminal/LocationUpdateParams.java b/src/main/java/com/stripe/param/terminal/LocationUpdateParams.java
index 98980336001..b0c8cbd1746 100644
--- a/src/main/java/com/stripe/param/terminal/LocationUpdateParams.java
+++ b/src/main/java/com/stripe/param/terminal/LocationUpdateParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class LocationUpdateParams extends ApiRequestParams {
   /** The full address of the location. */
@@ -20,6 +22,15 @@ public class LocationUpdateParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * To [group
    * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -29,10 +40,15 @@ public class LocationUpdateParams extends ApiRequestParams {
   String operatorAccount;
 
   private LocationUpdateParams(
-      Address address, String displayName, List<String> expand, String operatorAccount) {
+      Address address,
+      String displayName,
+      List<String> expand,
+      Map<String, Object> extraParams,
+      String operatorAccount) {
     this.address = address;
     this.displayName = displayName;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.operatorAccount = operatorAccount;
   }
 
@@ -47,12 +63,14 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String operatorAccount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public LocationUpdateParams build() {
       return new LocationUpdateParams(
-          this.address, this.displayName, this.expand, this.operatorAccount);
+          this.address, this.displayName, this.expand, this.extraParams, this.operatorAccount);
     }
 
     /** The full address of the location. */
@@ -93,6 +111,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * LocationUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link LocationUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * To [group
      * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -112,6 +156,15 @@ public static class Address {
     @SerializedName("country")
     String country;
 
+    /**
+     * Map of extra parameters for custom features not available in this client library. The content
+     * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+     * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+     * param object. Effectively, this map is flattened to its parent instance.
+     */
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    Map<String, Object> extraParams;
+
     @SerializedName("line1")
     String line1;
 
@@ -125,9 +178,16 @@ public static class Address {
     String state;
 
     private Address(
-        String city, String country, String line1, String line2, String postalCode, String state) {
+        String city,
+        String country,
+        Map<String, Object> extraParams,
+        String line1,
+        String line2,
+        String postalCode,
+        String state) {
       this.city = city;
       this.country = country;
+      this.extraParams = extraParams;
       this.line1 = line1;
       this.line2 = line2;
       this.postalCode = postalCode;
@@ -143,6 +203,8 @@ public static class Builder {
 
       private String country;
 
+      private Map<String, Object> extraParams;
+
       private String line1;
 
       private String line2;
@@ -154,7 +216,13 @@ public static class Builder {
       /** Finalize and obtain parameter instance from this builder. */
       public Address build() {
         return new Address(
-            this.city, this.country, this.line1, this.line2, this.postalCode, this.state);
+            this.city,
+            this.country,
+            this.extraParams,
+            this.line1,
+            this.line2,
+            this.postalCode,
+            this.state);
       }
 
       public Builder setCity(String city) {
@@ -167,6 +235,32 @@ public Builder setCountry(String country) {
         return this;
       }
 
+      /**
+       * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+       * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+       * LocationUpdateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putExtraParam(String key, Object value) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.put(key, value);
+        return this;
+      }
+
+      /**
+       * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+       * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+       * See {@link LocationUpdateParams.Address#extraParams} for the field documentation.
+       */
+      public Builder putAllExtraParam(Map<String, Object> map) {
+        if (this.extraParams == null) {
+          this.extraParams = new HashMap<>();
+        }
+        this.extraParams.putAll(map);
+        return this;
+      }
+
       public Builder setLine1(String line1) {
         this.line1 = line1;
         return this;
diff --git a/src/main/java/com/stripe/param/terminal/ReaderCreateParams.java b/src/main/java/com/stripe/param/terminal/ReaderCreateParams.java
index 79150e41323..2df0948c5c7 100644
--- a/src/main/java/com/stripe/param/terminal/ReaderCreateParams.java
+++ b/src/main/java/com/stripe/param/terminal/ReaderCreateParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReaderCreateParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * Custom label given to the reader for easier identification. If no label is specified, the
    * registration code will be used.
@@ -40,11 +51,13 @@ public class ReaderCreateParams extends ApiRequestParams {
 
   private ReaderCreateParams(
       List<String> expand,
+      Map<String, Object> extraParams,
       String label,
       String location,
       String operatorAccount,
       String registrationCode) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.label = label;
     this.location = location;
     this.operatorAccount = operatorAccount;
@@ -58,6 +71,8 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String label;
 
     private String location;
@@ -69,7 +84,12 @@ public static class Builder {
     /** Finalize and obtain parameter instance from this builder. */
     public ReaderCreateParams build() {
       return new ReaderCreateParams(
-          this.expand, this.label, this.location, this.operatorAccount, this.registrationCode);
+          this.expand,
+          this.extraParams,
+          this.label,
+          this.location,
+          this.operatorAccount,
+          this.registrationCode);
     }
 
     /**
@@ -98,6 +118,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReaderCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReaderCreateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * Custom label given to the reader for easier identification. If no label is specified, the
      * registration code will be used.
diff --git a/src/main/java/com/stripe/param/terminal/ReaderDeleteParams.java b/src/main/java/com/stripe/param/terminal/ReaderDeleteParams.java
index c19707a0a15..072d08baca7 100644
--- a/src/main/java/com/stripe/param/terminal/ReaderDeleteParams.java
+++ b/src/main/java/com/stripe/param/terminal/ReaderDeleteParams.java
@@ -4,8 +4,19 @@
 
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
+import java.util.HashMap;
+import java.util.Map;
 
 public class ReaderDeleteParams extends ApiRequestParams {
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * To [group
    * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -14,7 +25,8 @@ public class ReaderDeleteParams extends ApiRequestParams {
   @SerializedName("operator_account")
   String operatorAccount;
 
-  private ReaderDeleteParams(String operatorAccount) {
+  private ReaderDeleteParams(Map<String, Object> extraParams, String operatorAccount) {
+    this.extraParams = extraParams;
     this.operatorAccount = operatorAccount;
   }
 
@@ -23,11 +35,39 @@ public static Builder builder() {
   }
 
   public static class Builder {
+    private Map<String, Object> extraParams;
+
     private String operatorAccount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ReaderDeleteParams build() {
-      return new ReaderDeleteParams(this.operatorAccount);
+      return new ReaderDeleteParams(this.extraParams, this.operatorAccount);
+    }
+
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReaderDeleteParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReaderDeleteParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
     }
 
     /**
diff --git a/src/main/java/com/stripe/param/terminal/ReaderListParams.java b/src/main/java/com/stripe/param/terminal/ReaderListParams.java
index 66dc73200e5..8c023fcf65d 100644
--- a/src/main/java/com/stripe/param/terminal/ReaderListParams.java
+++ b/src/main/java/com/stripe/param/terminal/ReaderListParams.java
@@ -5,7 +5,9 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReaderListParams extends ApiRequestParams {
   /**
@@ -21,6 +23,15 @@ public class ReaderListParams extends ApiRequestParams {
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
    * default is 10.
@@ -56,6 +67,7 @@ public class ReaderListParams extends ApiRequestParams {
   private ReaderListParams(
       String endingBefore,
       List<String> expand,
+      Map<String, Object> extraParams,
       Long limit,
       String location,
       String operatorAccount,
@@ -63,6 +75,7 @@ private ReaderListParams(
       String status) {
     this.endingBefore = endingBefore;
     this.expand = expand;
+    this.extraParams = extraParams;
     this.limit = limit;
     this.location = location;
     this.operatorAccount = operatorAccount;
@@ -79,6 +92,8 @@ public static class Builder {
 
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private Long limit;
 
     private String location;
@@ -94,6 +109,7 @@ public ReaderListParams build() {
       return new ReaderListParams(
           this.endingBefore,
           this.expand,
+          this.extraParams,
           this.limit,
           this.location,
           this.operatorAccount,
@@ -138,6 +154,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReaderListParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReaderListParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * A limit on the number of objects to be returned. Limit can range between 1 and 100, and the
      * default is 10.
diff --git a/src/main/java/com/stripe/param/terminal/ReaderRetrieveParams.java b/src/main/java/com/stripe/param/terminal/ReaderRetrieveParams.java
index 336c2f7d21a..945964f56ff 100644
--- a/src/main/java/com/stripe/param/terminal/ReaderRetrieveParams.java
+++ b/src/main/java/com/stripe/param/terminal/ReaderRetrieveParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReaderRetrieveParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /**
    * To [group
    * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
@@ -20,8 +31,10 @@ public class ReaderRetrieveParams extends ApiRequestParams {
   @SerializedName("operator_account")
   String operatorAccount;
 
-  private ReaderRetrieveParams(List<String> expand, String operatorAccount) {
+  private ReaderRetrieveParams(
+      List<String> expand, Map<String, Object> extraParams, String operatorAccount) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.operatorAccount = operatorAccount;
   }
 
@@ -32,11 +45,13 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String operatorAccount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ReaderRetrieveParams build() {
-      return new ReaderRetrieveParams(this.expand, this.operatorAccount);
+      return new ReaderRetrieveParams(this.expand, this.extraParams, this.operatorAccount);
     }
 
     /**
@@ -65,6 +80,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReaderRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReaderRetrieveParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /**
      * To [group
      * objects](https://stripe.com/docs/terminal/payments/connect#grouping-objects-by-connected-account)
diff --git a/src/main/java/com/stripe/param/terminal/ReaderUpdateParams.java b/src/main/java/com/stripe/param/terminal/ReaderUpdateParams.java
index 1fbd7ee37ef..94955aa8d61 100644
--- a/src/main/java/com/stripe/param/terminal/ReaderUpdateParams.java
+++ b/src/main/java/com/stripe/param/terminal/ReaderUpdateParams.java
@@ -5,13 +5,24 @@
 import com.google.gson.annotations.SerializedName;
 import com.stripe.net.ApiRequestParams;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class ReaderUpdateParams extends ApiRequestParams {
   /** Specifies which fields in the response should be expanded. */
   @SerializedName("expand")
   List<String> expand;
 
+  /**
+   * Map of extra parameters for custom features not available in this client library. The content
+   * in this map is not serialized under this field's {@code @SerializedName} value. Instead, each
+   * key/value pair is serialized as if the key is a root-level field (serialized) name in this
+   * param object. Effectively, this map is flattened to its parent instance.
+   */
+  @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+  Map<String, Object> extraParams;
+
   /** The new label of the reader. */
   @SerializedName("label")
   String label;
@@ -24,8 +35,10 @@ public class ReaderUpdateParams extends ApiRequestParams {
   @SerializedName("operator_account")
   String operatorAccount;
 
-  private ReaderUpdateParams(List<String> expand, String label, String operatorAccount) {
+  private ReaderUpdateParams(
+      List<String> expand, Map<String, Object> extraParams, String label, String operatorAccount) {
     this.expand = expand;
+    this.extraParams = extraParams;
     this.label = label;
     this.operatorAccount = operatorAccount;
   }
@@ -37,13 +50,16 @@ public static Builder builder() {
   public static class Builder {
     private List<String> expand;
 
+    private Map<String, Object> extraParams;
+
     private String label;
 
     private String operatorAccount;
 
     /** Finalize and obtain parameter instance from this builder. */
     public ReaderUpdateParams build() {
-      return new ReaderUpdateParams(this.expand, this.label, this.operatorAccount);
+      return new ReaderUpdateParams(
+          this.expand, this.extraParams, this.label, this.operatorAccount);
     }
 
     /**
@@ -72,6 +88,32 @@ public Builder addAllExpand(List<String> elements) {
       return this;
     }
 
+    /**
+     * Add a key/value pair to `extraParams` map. A map is initialized for the first `put/putAll`
+     * call, and subsequent calls add additional key/value pairs to the original map. See {@link
+     * ReaderUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putExtraParam(String key, Object value) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.put(key, value);
+      return this;
+    }
+
+    /**
+     * Add all map key/value pairs to `extraParams` map. A map is initialized for the first
+     * `put/putAll` call, and subsequent calls add additional key/value pairs to the original map.
+     * See {@link ReaderUpdateParams#extraParams} for the field documentation.
+     */
+    public Builder putAllExtraParam(Map<String, Object> map) {
+      if (this.extraParams == null) {
+        this.extraParams = new HashMap<>();
+      }
+      this.extraParams.putAll(map);
+      return this;
+    }
+
     /** The new label of the reader. */
     public Builder setLabel(String label) {
       this.label = label;
diff --git a/src/test/java/com/stripe/functional/InvoiceTest.java b/src/test/java/com/stripe/functional/InvoiceTest.java
index d1852748610..4c2039bede7 100644
--- a/src/test/java/com/stripe/functional/InvoiceTest.java
+++ b/src/test/java/com/stripe/functional/InvoiceTest.java
@@ -4,19 +4,23 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.common.collect.ImmutableMap;
+
 import com.stripe.BaseStripeTest;
 import com.stripe.exception.StripeException;
 import com.stripe.model.Invoice;
 import com.stripe.model.InvoiceCollection;
 import com.stripe.net.ApiResource;
-
 import com.stripe.net.RequestOptions;
+import com.stripe.param.InvoiceCreateParams;
 import com.stripe.param.InvoiceUpcomingParams;
 import com.stripe.param.InvoiceUpdateParams;
 import com.stripe.param.common.EmptyParam;
+
 import java.math.BigDecimal;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import org.junit.jupiter.api.Test;
@@ -77,7 +81,7 @@ public void testUpdate() throws StripeException {
   }
 
   @Test
-  public void testUpdateWithTypeParams() throws StripeException {
+  public void testUpdateWithTypedParams() throws StripeException {
     final Invoice invoice = getInvoiceFixture();
 
     final Map<String, String> metadata = new HashMap<>();
@@ -114,13 +118,17 @@ public void testUpdateWithTypeParams() throws StripeException {
         String.format("/v1/invoices/%s", invoice.getId()),
         params
     );
+  }
 
+  @Test
+  public void testUpdateWithTypedParamsContainingEmptyParamEnum() throws StripeException {
+    final Invoice invoice = getInvoiceFixture();
     InvoiceUpdateParams typedParamsWithEmpty = InvoiceUpdateParams.builder()
         .setCustomFields(EmptyParam.EMPTY)
         .setTaxPercent(EmptyParam.EMPTY)
         .build();
 
-    updatedInvoice = invoice.update(typedParamsWithEmpty, RequestOptions.getDefault());
+    Invoice updatedInvoice = invoice.update(typedParamsWithEmpty, RequestOptions.getDefault());
 
     Map<String, Object> paramsWithEmpty = new HashMap<>();
     paramsWithEmpty.put("custom_fields", null);
@@ -134,6 +142,49 @@ public void testUpdateWithTypeParams() throws StripeException {
     );
   }
 
+  @Test
+  public void testUpdateWithExtraParams() throws StripeException {
+    final Invoice invoice = getInvoiceFixture();
+    // suppose that `custom_fields` isn't available yet, pretend
+    // that users want this beta feature and use untyped map in our
+    // main typed param via `putExtraParam`
+    List<Map<String, Object>> customFields = new ArrayList<>();
+    customFields.add(
+        ImmutableMap.of(
+            "name", "A",
+            "value", "1"
+        ));
+    customFields.add(
+        ImmutableMap.of(
+            "name", "B",
+            "value", "2"
+        )
+    );
+
+    InvoiceUpdateParams paramsWithExtraParam = InvoiceUpdateParams.builder()
+        .putExtraParam("custom_fields", customFields)
+        .build();
+
+    Invoice updatedInvoice = invoice.update(paramsWithExtraParam, RequestOptions.getDefault());
+
+    assertNotNull(updatedInvoice);
+
+    assertNotNull(invoice);
+    verifyRequest(
+        ApiResource.RequestMethod.POST,
+        String.format("/v1/invoices/%s", invoice.getId()),
+        // param with extra param has the same map as that using standard builder
+        InvoiceCreateParams.builder()
+            .setCustomFields(Arrays.asList(
+                InvoiceCreateParams.CustomField.builder()
+                    .setName("A").setValue("1").build(),
+                InvoiceCreateParams.CustomField.builder()
+                    .setName("B").setValue("2").build()
+            ))
+            .build().toMap()
+    );
+  }
+
   @Test
   public void testList() throws StripeException {
     final Map<String, Object> params = new HashMap<>();
diff --git a/src/test/java/com/stripe/net/ApiRequestParamsConverterTest.java b/src/test/java/com/stripe/net/ApiRequestParamsConverterTest.java
new file mode 100644
index 00000000000..c9b3d57875e
--- /dev/null
+++ b/src/test/java/com/stripe/net/ApiRequestParamsConverterTest.java
@@ -0,0 +1,221 @@
+package com.stripe.net;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.google.gson.annotations.SerializedName;
+
+import com.stripe.param.common.EmptyParam;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+public class ApiRequestParamsConverterTest {
+  private ApiRequestParamsConverter converter = new ApiRequestParamsConverter();
+
+  // To test interactions between the flattening and empty enums
+  enum ParamCode implements ApiRequestParams.EnumParam {
+    ENUM_FOO("enum_foo"),
+    ENUM_BAR("enum_bar"),;
+
+    private final String value;
+
+    ParamCode(String value) {
+      this.value = value;
+    }
+
+    @Override
+    public String getValue() {
+      return this.value;
+    }
+  }
+
+  // The fields are implicitly used in testing serialization
+  @SuppressWarnings("UnusedVariable")
+  private static class ModelHasExtraParams extends ApiRequestParams {
+    private String stringValue;
+    private EnumParam enumValue;
+
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    private Map<String, Object> extraParams;
+
+    public ModelHasExtraParams(EnumParam enumValue) {
+      this.stringValue = "foo";
+      this.enumValue = enumValue;
+      this.extraParams = new HashMap<>();
+      this.extraParams.put("hello", "world");
+    }
+
+    static Map<String, Object> expectedParams(String enumString) {
+      Map<String, Object> paramMap = new HashMap<>();
+      paramMap.put("string_value", "foo");
+      paramMap.put("enum_value", enumString);
+      // "hello" key is flattened to the same level as root-level params
+      // and the key for `extraParams` is dropped
+      paramMap.put("hello", "world");
+      return paramMap;
+    }
+  }
+
+  // The fields are implicitly used in testing serialization
+  @SuppressWarnings("UnusedVariable")
+  private static class RootModelHasNestedExtraParams extends ApiRequestParams {
+    private String rootStringValue;
+    private EnumParam rootEnumValue;
+    private ModelHasExtraParams subParamFoo;
+
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    private Map<String, String> extraParams;
+
+    public RootModelHasNestedExtraParams(EnumParam rootEnumValue,
+                                         ModelHasExtraParams subParamFoo) {
+      this.rootStringValue = "bar";
+      this.rootEnumValue = rootEnumValue;
+      this.subParamFoo = subParamFoo;
+      this.extraParams = new HashMap<>();
+      this.extraParams.put("bar_hello", "bar_world");
+    }
+
+    static Map<String, Object> expectedParams(String enumString) {
+      Map<String, Object> rootLevelParams = new HashMap<>();
+      rootLevelParams.put("root_string_value", "bar");
+      rootLevelParams.put("root_enum_value", enumString);
+      // similar to the `ModelHasExtraParams` test model,
+      // "bar_hello" key is flattened to the same level as root-level params
+      rootLevelParams.put("bar_hello", "bar_world");
+      return rootLevelParams;
+    }
+  }
+
+  private static class ModelHasListExtraParams extends ApiRequestParams {
+    List<ModelHasExtraParams> paramFooList;
+  }
+
+  private static class ModelHasExtraParamsWithWrongSerializedName extends ApiRequestParams {
+    @SerializedName("extra_params")
+    private Map<String, String> extraParams;
+  }
+
+  private static class IllegalModelHasWrongExtraParamsType extends ApiRequestParams {
+    @SerializedName(ApiRequestParams.EXTRA_PARAMS_KEY)
+    String extraParams;
+  }
+
+  @Test
+  public void testHasExtraParams() {
+    ModelHasExtraParams params = new ModelHasExtraParams(ParamCode.ENUM_FOO);
+
+    assertEquals(
+        ModelHasExtraParams.expectedParams("enum_foo"),
+        toMap(params));
+  }
+
+  @Test
+  public void testHasExtraParamsWithFormEncodedKeys() {
+    ModelHasExtraParams params = new ModelHasExtraParams(ParamCode.ENUM_FOO);
+    params.extraParams.put("root_param[foo][string]", "value_foo");
+    params.extraParams.put("root_param[bar][integer]", "123");
+
+    Map<String, Object> expected = ModelHasExtraParams.expectedParams("enum_foo");
+    assertNotEquals(expected, toMap(params));
+
+    expected.put("root_param[foo][string]", "value_foo");
+    expected.put("root_param[bar][integer]", "123");
+    assertEquals(expected, toMap(params));
+  }
+
+  @Test
+  public void testHasNestedExtraParams() {
+    ModelHasExtraParams fooParams = new ModelHasExtraParams(ParamCode.ENUM_FOO);
+    RootModelHasNestedExtraParams barParams = new RootModelHasNestedExtraParams(
+        ParamCode.ENUM_BAR, fooParams);
+
+    Map<String, Object> expected = RootModelHasNestedExtraParams
+        .expectedParams("enum_bar");
+    expected.put("sub_param_foo", ModelHasExtraParams.expectedParams("enum_foo"));
+
+    assertEquals(expected, toMap(barParams));
+  }
+
+  @Test
+  public void testHasNestedExtraParamsWithEmpty() {
+    ModelHasExtraParams fooParams = new ModelHasExtraParams(EmptyParam.EMPTY);
+
+    RootModelHasNestedExtraParams barParams = new RootModelHasNestedExtraParams(
+        EmptyParam.EMPTY, fooParams);
+
+    Map<String, Object> expected = RootModelHasNestedExtraParams.expectedParams(null);
+    expected.put("sub_param_foo", ModelHasExtraParams.expectedParams(null));
+
+    assertEquals(expected, toMap(barParams));
+  }
+
+  @Test
+  public void testHasListExtraParams() {
+    ModelHasListExtraParams params = new ModelHasListExtraParams();
+    params.paramFooList = Arrays.asList(
+        new ModelHasExtraParams(ParamCode.ENUM_FOO),
+        new ModelHasExtraParams(ParamCode.ENUM_BAR)
+    );
+
+    Map<String, Object> expected = new HashMap<>();
+    expected.put("param_foo_list",
+        Arrays.asList(
+            ModelHasExtraParams.expectedParams("enum_foo"),
+            ModelHasExtraParams.expectedParams("enum_bar")
+        ));
+    assertEquals(expected, toMap(params));
+  }
+
+  @SuppressWarnings("unchecked")
+  @Test
+  public void testHasExtraParamsWithWrongSerializedName() {
+    ModelHasExtraParamsWithWrongSerializedName params =
+        new ModelHasExtraParamsWithWrongSerializedName();
+    params.extraParams = new HashMap<>();
+    params.extraParams.put("foo", "bar");
+
+    Map<String, Object> untypedParams = toMap(params);
+    assertEquals(1, untypedParams.size());
+    assertTrue(untypedParams.containsKey("extra_params"));
+    Map<String, Object> subParams = (Map<String, Object>)untypedParams.get("extra_params");
+    assertEquals(1, subParams.size());
+    assertEquals("bar", subParams.get("foo"));
+  }
+
+  @Test
+  public void testIllegalExtraParamsType() {
+    IllegalModelHasWrongExtraParamsType params = new IllegalModelHasWrongExtraParamsType();
+    params.extraParams = "should have been a map";
+
+    IllegalStateException exception = assertThrows(IllegalStateException.class, () -> {
+      toMap(params);
+    });
+    assertTrue(exception.getMessage().contains("Unexpected schema for extra params"));
+  }
+
+  @Test
+  public void testIllegalConflictingExtraParams() {
+    ModelHasExtraParams fooParams = new ModelHasExtraParams(ParamCode.ENUM_FOO);
+    // `string_value` will find two param values: one from the original param, the other from the
+    // flattened extra param map.
+    assertTrue(fooParams.toMap().containsKey("string_value"));
+    fooParams.extraParams.put("string_value", "my conflicting param value");
+
+    IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> {
+      toMap(fooParams);
+    });
+    assertTrue(exception.getMessage().contains(
+        "Found param key `string_value` with values `foo` and `my conflicting param value`."));
+  }
+
+  private Map<String, Object> toMap(ApiRequestParams params) {
+    return converter.convert(params);
+  }
+}
\ No newline at end of file
diff --git a/src/test/java/com/stripe/net/LiveStripeResponseGetterTest.java b/src/test/java/com/stripe/net/LiveStripeResponseGetterTest.java
index e8c3672e639..f7352979de9 100644
--- a/src/test/java/com/stripe/net/LiveStripeResponseGetterTest.java
+++ b/src/test/java/com/stripe/net/LiveStripeResponseGetterTest.java
@@ -123,6 +123,27 @@ public void testCreateQueryWithListOfHashes() throws StripeException,
         LiveStripeResponseGetter.createQuery(params));
   }
 
+  @Test
+  public void testCreateQueryWithFormEncodedKeys() throws StripeException,
+      UnsupportedEncodingException {
+    /* Use LinkedHashMap because it preserves iteration order */
+    final Map<String, Object> params = new LinkedHashMap<>();
+
+    // Params with form-encoded keys can happen through "extraParams". Instead of passing a
+    // string key and `Object` value, users can also specify key as form-encoded path to the
+    // extra param value.
+    // This "extraParams" behavior is supported by other typed libraries, but not
+    // intended in `stripe-java`. However, by the virtue of supporting arbitrary string key in
+    // extra param map, this behavior is implicitly supported.
+    params.put("nested[0][A]", "A-1");
+    params.put("nested[0][B]", "B-1");
+    params.put("nested[1][A]", "A-2");
+    params.put("nested[1][B]", "B-2");
+
+    assertEquals("nested[0][A]=A-1&nested[0][B]=B-1&nested[1][A]=A-2&nested[1][B]=B-2",
+        LiveStripeResponseGetter.createQuery(params));
+  }
+
   @SuppressWarnings("ModifiedButNotUsed")
   @Test
   public void testCreateQueryWithCollection() throws UnsupportedEncodingException,
diff --git a/src/test/java/com/stripe/net/UntypedMapDeserializerTest.java b/src/test/java/com/stripe/net/UntypedMapDeserializerTest.java
index ce4472a812d..2fd6da100b6 100644
--- a/src/test/java/com/stripe/net/UntypedMapDeserializerTest.java
+++ b/src/test/java/com/stripe/net/UntypedMapDeserializerTest.java
@@ -1,6 +1,6 @@
 package com.stripe.net;
 
-import static org.junit.Assert.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 import com.google.common.collect.ImmutableMap;
 import com.google.gson.JsonArray;
@@ -10,15 +10,29 @@
 import com.google.gson.JsonPrimitive;
 
 import java.math.BigDecimal;
+import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 public class UntypedMapDeserializerTest {
 
   private UntypedMapDeserializer untypedMapDeserializer = new UntypedMapDeserializer();
 
+  private UntypedMapDeserializer flatteningDeserializer = new UntypedMapDeserializer(
+      (outerMap, jsonEntry, untypedMapDeserializer) -> {
+        JsonElement value = jsonEntry.getValue();
+        if (value.isJsonObject()) {
+          outerMap.putAll(untypedMapDeserializer.deserialize(value.getAsJsonObject()));
+        } else {
+          outerMap.put(jsonEntry.getKey(),
+              untypedMapDeserializer.deserializeJsonElement(value));
+        }
+        return;
+      }
+  );
+
   @Test
   @SuppressWarnings("unchecked")
   public void testMapOfArray() {
@@ -90,6 +104,50 @@ public void testMapOfArrayOfMap() {
     assertEquals(ImmutableMap.of("bar", 3L), objects.get(1));
   }
 
+  @Test
+  public void tesStrategyFlattenAllSchema() {
+    // {"parent": {"child": {"grand_child": 1}}}
+    JsonObject jsonObject = new JsonObject();
+    jsonObject.add("parent",
+        jsonObject("child", jsonObject("grand_child", jsonNumber(1L))));
+    Map<String, Object> untyped = flatteningDeserializer.deserialize(jsonObject);
+    // innermost remains
+    assertEquals(ImmutableMap.of("grand_child", 1L), untyped);
+  }
+
+  @Test
+  public void tesStrategyFlattenInArraySchema() {
+    JsonArray jsonArray = jsonArray(
+        jsonObject("child", jsonObject("grand_child", jsonNumber(1L))),
+        jsonObject("child", jsonObject("grand_child", jsonNumber(2L))),
+        jsonObject("child", jsonObject("grand_child", jsonNumber(3L)))
+    );
+
+    Object untyped = flatteningDeserializer.deserializeJsonElement(jsonArray);
+    assertEquals(Arrays.asList(
+        ImmutableMap.of("grand_child", 1L),
+        ImmutableMap.of("grand_child", 2L),
+        ImmutableMap.of("grand_child", 3L)), untyped);
+  }
+
+  @Test
+  public void tesStrategyRenameKey() {
+    UntypedMapDeserializer renamer = new UntypedMapDeserializer(
+        (outerMap, jsonEntry, untypedMapDeserializer) -> {
+          JsonElement value = jsonEntry.getValue();
+          outerMap.put(jsonEntry.getKey() + "_foo",
+              untypedMapDeserializer.deserializeJsonElement(value));
+        }
+    );
+
+    JsonObject jsonObject = new JsonObject();
+    jsonObject.add("child", jsonObject("grand_child", jsonNumber(1L)));
+    Map<String, Object> untyped = renamer.deserialize(jsonObject);
+    assertEquals(untyped, ImmutableMap.of(
+        "child_foo", ImmutableMap.of("grand_child_foo", 1L)
+    ));
+  }
+
   private JsonArray jsonArray(JsonElement... elements) {
     JsonArray jsonArray = new JsonArray();
     for (JsonElement primitive : elements) {
@@ -111,4 +169,4 @@ private JsonObject jsonObject(String key, JsonElement element) {
     jsonObject.add(key, element);
     return jsonObject;
   }
-}
+}
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