diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Batch.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Batch.java
index eb4abd854..c9a01673d 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Batch.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Batch.java
@@ -16,6 +16,7 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import java.util.List;
 import javax.annotation.concurrent.NotThreadSafe;
 
@@ -42,6 +43,7 @@
  * This class too should not be treated as a thread safe class. </b>
  */
 @NotThreadSafe
+@InternalExtensionOnly
 public interface Batch extends DatastoreBatchWriter {
 
   interface Response {
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Datastore.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Datastore.java
index 1fb5fcedc..fc368506e 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Datastore.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Datastore.java
@@ -16,12 +16,14 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import com.google.cloud.Service;
 import com.google.datastore.v1.TransactionOptions;
 import java.util.Iterator;
 import java.util.List;
 
 /** An interface for Google Cloud Datastore. */
+@InternalExtensionOnly
 public interface Datastore extends Service<DatastoreOptions>, DatastoreReaderWriter, AutoCloseable {
 
   /**
@@ -505,9 +507,7 @@ interface TransactionCallable<T> {
    * @throws DatastoreException upon failure
    * @return {@link AggregationResults}
    */
-  default AggregationResults runAggregation(AggregationQuery query, ReadOption... options) {
-    throw new UnsupportedOperationException("Not implemented.");
-  }
+  AggregationResults runAggregation(AggregationQuery query, ReadOption... options);
 
   /**
    * Closes the gRPC channels associated with this instance and frees up their resources. This
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreBatchWriter.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreBatchWriter.java
index db4bd3179..28d2569b6 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreBatchWriter.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreBatchWriter.java
@@ -16,6 +16,7 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import java.util.List;
 import javax.annotation.concurrent.NotThreadSafe;
 
@@ -31,6 +32,7 @@
  * This class too should not be treated as a thread safe class. </b>
  */
 @NotThreadSafe
+@InternalExtensionOnly
 public interface DatastoreBatchWriter extends DatastoreWriter {
 
   /**
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreFactory.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreFactory.java
index 1b443066d..54274e7bb 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreFactory.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreFactory.java
@@ -16,7 +16,9 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import com.google.cloud.ServiceFactory;
 
 /** An interface for Datastore factories. */
+@InternalExtensionOnly
 public interface DatastoreFactory extends ServiceFactory<Datastore, DatastoreOptions> {}
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreReader.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreReader.java
index 2a3071f3c..e8e5d3b03 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreReader.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreReader.java
@@ -16,10 +16,12 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import java.util.Iterator;
 import java.util.List;
 
 /** An interface to represent Google Cloud Datastore read operations. */
+@InternalExtensionOnly
 public interface DatastoreReader {
 
   /**
@@ -59,7 +61,5 @@ public interface DatastoreReader {
    *
    * @throws DatastoreException upon failure
    */
-  default AggregationResults runAggregation(AggregationQuery query) {
-    throw new UnsupportedOperationException("Not implemented.");
-  }
+  AggregationResults runAggregation(AggregationQuery query);
 }
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreReaderWriter.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreReaderWriter.java
index a51a5aa77..bc8700c70 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreReaderWriter.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreReaderWriter.java
@@ -16,5 +16,8 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
+
 /** An interface that combines both Google Cloud Datastore read and write operations. */
+@InternalExtensionOnly
 public interface DatastoreReaderWriter extends DatastoreReader, DatastoreWriter {}
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreWriter.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreWriter.java
index 6c1d6fdbc..b414995e6 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreWriter.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/DatastoreWriter.java
@@ -16,9 +16,11 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import java.util.List;
 
 /** An interface to represent Google Cloud Datastore write operations. */
+@InternalExtensionOnly
 public interface DatastoreWriter {
 
   /**
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/QueryResults.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/QueryResults.java
index 3f73824dc..b42e33d1a 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/QueryResults.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/QueryResults.java
@@ -16,6 +16,7 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import com.google.datastore.v1.QueryResultBatch;
 import java.util.Iterator;
 
@@ -28,6 +29,7 @@
  *
  * @param <V> the type of the results value.
  */
+@InternalExtensionOnly
 public interface QueryResults<V> extends Iterator<V> {
 
   /** Returns the actual class of the result's values. */
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/StructuredQuery.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/StructuredQuery.java
index 30cd05759..5bde80ed6 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/StructuredQuery.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/StructuredQuery.java
@@ -27,6 +27,7 @@
 
 import com.google.api.core.ApiFunction;
 import com.google.api.core.InternalApi;
+import com.google.api.core.InternalExtensionOnly;
 import com.google.cloud.StringEnumType;
 import com.google.cloud.StringEnumValue;
 import com.google.cloud.Timestamp;
@@ -700,6 +701,7 @@ public String toString() {
    *
    * @param <V> the type of result the query returns.
    */
+  @InternalExtensionOnly
   public interface Builder<V> {
 
     /** Sets the namespace for the query. */
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Transaction.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Transaction.java
index 69c18d75c..f68c3889b 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Transaction.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/Transaction.java
@@ -16,6 +16,7 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import com.google.protobuf.ByteString;
 import java.util.Iterator;
 import java.util.List;
@@ -61,6 +62,7 @@
  *     This class too should not be treated as a thread safe class. </b>
  */
 @NotThreadSafe
+@InternalExtensionOnly
 public interface Transaction extends DatastoreBatchWriter, DatastoreReaderWriter {
 
   interface Response {
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/ValueBuilder.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/ValueBuilder.java
index 3c60ef409..315728147 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/ValueBuilder.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/ValueBuilder.java
@@ -16,6 +16,7 @@
 
 package com.google.cloud.datastore;
 
+import com.google.api.core.InternalExtensionOnly;
 import com.google.cloud.GcpLaunchStage;
 
 /**
@@ -25,6 +26,7 @@
  * @param <P> the value type.
  * @param <B> the value type's associated builder.
  */
+@InternalExtensionOnly
 public interface ValueBuilder<V, P extends Value<V>, B extends ValueBuilder<V, P, B>> {
 
   ValueType getValueType();
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/aggregation/AggregationBuilder.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/aggregation/AggregationBuilder.java
index ce23edcf0..632f44393 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/aggregation/AggregationBuilder.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/aggregation/AggregationBuilder.java
@@ -16,6 +16,8 @@
 
 package com.google.cloud.datastore.aggregation;
 
+import com.google.api.core.InternalExtensionOnly;
+
 /**
  * An interface to represent the builders which build and customize {@link Aggregation} for {@link
  * com.google.cloud.datastore.AggregationQuery}.
@@ -23,6 +25,7 @@
  * <p>Used by {@link
  * com.google.cloud.datastore.AggregationQuery.Builder#addAggregation(AggregationBuilder)}.
  */
+@InternalExtensionOnly
 public interface AggregationBuilder<A extends Aggregation> {
   A build();
 }
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/DatastoreRpcFactory.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/DatastoreRpcFactory.java
index 0b7f9094b..acb85a61d 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/DatastoreRpcFactory.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/DatastoreRpcFactory.java
@@ -16,6 +16,7 @@
 
 package com.google.cloud.datastore.spi;
 
+import com.google.api.core.InternalExtensionOnly;
 import com.google.cloud.datastore.DatastoreOptions;
 import com.google.cloud.spi.ServiceRpcFactory;
 
@@ -23,4 +24,5 @@
  * An interface for Datastore RPC factory. Implementation will be loaded via {@link
  * java.util.ServiceLoader}.
  */
+@InternalExtensionOnly
 public interface DatastoreRpcFactory extends ServiceRpcFactory<DatastoreOptions> {}
diff --git a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/v1/DatastoreRpc.java b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/v1/DatastoreRpc.java
index 1f73429f8..3b163f6fd 100644
--- a/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/v1/DatastoreRpc.java
+++ b/google-cloud-datastore/src/main/java/com/google/cloud/datastore/spi/v1/DatastoreRpc.java
@@ -17,6 +17,7 @@
 package com.google.cloud.datastore.spi.v1;
 
 import com.google.api.core.InternalApi;
+import com.google.api.core.InternalExtensionOnly;
 import com.google.api.gax.rpc.HeaderProvider;
 import com.google.cloud.ServiceRpc;
 import com.google.cloud.datastore.DatastoreException;
@@ -39,6 +40,7 @@
 import com.google.datastore.v1.RunQueryResponse;
 
 /** Provides access to the remote Datastore service. */
+@InternalExtensionOnly
 public interface DatastoreRpc extends ServiceRpc, AutoCloseable {
 
   /**
@@ -96,9 +98,7 @@ BeginTransactionResponse beginTransaction(BeginTransactionRequest request)
    *
    * @throws DatastoreException upon failure
    */
-  default RunAggregationQueryResponse runAggregationQuery(RunAggregationQueryRequest request) {
-    throw new UnsupportedOperationException("Not implemented.");
-  }
+  RunAggregationQueryResponse runAggregationQuery(RunAggregationQueryRequest request);
 
   @Override
   void close() throws Exception;