diff --git a/src/agents/extensions/models/litellm_model.py b/src/agents/extensions/models/litellm_model.py
index 0fc277c3..c72664a4 100644
--- a/src/agents/extensions/models/litellm_model.py
+++ b/src/agents/extensions/models/litellm_model.py
@@ -286,7 +286,7 @@ async def _fetch_response(
             stream=stream,
             stream_options=stream_options,
             reasoning_effort=reasoning_effort,
-            extra_headers=HEADERS,
+            extra_headers={**HEADERS, **(model_settings.extra_headers or {})},
             api_key=self.api_key,
             base_url=self.base_url,
             **extra_kwargs,
diff --git a/src/agents/model_settings.py b/src/agents/model_settings.py
index ed9a0131..fee92b4e 100644
--- a/src/agents/model_settings.py
+++ b/src/agents/model_settings.py
@@ -3,7 +3,7 @@
 from dataclasses import dataclass, fields, replace
 from typing import Literal
 
-from openai._types import Body, Query
+from openai._types import Body, Headers, Query
 from openai.types.shared import Reasoning
 
 
@@ -67,6 +67,10 @@ class ModelSettings:
     """Additional body fields to provide with the request.
     Defaults to None if not provided."""
 
+    extra_headers: Headers | None = None
+    """Additional headers to provide with the request.
+    Defaults to None if not provided."""
+
     def resolve(self, override: ModelSettings | None) -> ModelSettings:
         """Produce a new ModelSettings by overlaying any non-None values from the
         override on top of this instance."""
diff --git a/src/agents/models/openai_chatcompletions.py b/src/agents/models/openai_chatcompletions.py
index 9989c1ee..e0882927 100644
--- a/src/agents/models/openai_chatcompletions.py
+++ b/src/agents/models/openai_chatcompletions.py
@@ -255,7 +255,7 @@ async def _fetch_response(
             stream_options=self._non_null_or_not_given(stream_options),
             store=self._non_null_or_not_given(store),
             reasoning_effort=self._non_null_or_not_given(reasoning_effort),
-            extra_headers=HEADERS,
+            extra_headers={ **HEADERS, **(model_settings.extra_headers or {}) },
             extra_query=model_settings.extra_query,
             extra_body=model_settings.extra_body,
             metadata=self._non_null_or_not_given(model_settings.metadata),
diff --git a/src/agents/models/openai_responses.py b/src/agents/models/openai_responses.py
index ab4617d4..5f067296 100644
--- a/src/agents/models/openai_responses.py
+++ b/src/agents/models/openai_responses.py
@@ -253,7 +253,7 @@ async def _fetch_response(
             tool_choice=tool_choice,
             parallel_tool_calls=parallel_tool_calls,
             stream=stream,
-            extra_headers=_HEADERS,
+            extra_headers={**_HEADERS, **(model_settings.extra_headers or {})},
             extra_query=model_settings.extra_query,
             extra_body=model_settings.extra_body,
             text=response_format,
diff --git a/tests/test_extra_headers.py b/tests/test_extra_headers.py
new file mode 100644
index 00000000..f29c2540
--- /dev/null
+++ b/tests/test_extra_headers.py
@@ -0,0 +1,92 @@
+import pytest
+from openai.types.chat.chat_completion import ChatCompletion, Choice
+from openai.types.chat.chat_completion_message import ChatCompletionMessage
+
+from agents import ModelSettings, ModelTracing, OpenAIChatCompletionsModel, OpenAIResponsesModel
+
+
+@pytest.mark.allow_call_model_methods
+@pytest.mark.asyncio
+async def test_extra_headers_passed_to_openai_responses_model():
+    """
+    Ensure extra_headers in ModelSettings is passed to the OpenAIResponsesModel client.
+    """
+    called_kwargs = {}
+
+    class DummyResponses:
+        async def create(self, **kwargs):
+            nonlocal called_kwargs
+            called_kwargs = kwargs
+            class DummyResponse:
+                id = "dummy"
+                output = []
+                usage = type(
+                    "Usage", (), {"input_tokens": 0, "output_tokens": 0, "total_tokens": 0}
+                )()
+            return DummyResponse()
+
+    class DummyClient:
+        def __init__(self):
+            self.responses = DummyResponses()
+
+
+
+    model = OpenAIResponsesModel(model="gpt-4", openai_client=DummyClient()) # type: ignore
+    extra_headers = {"X-Test-Header": "test-value"}
+    await model.get_response(
+        system_instructions=None,
+        input="hi",
+        model_settings=ModelSettings(extra_headers=extra_headers),
+        tools=[],
+        output_schema=None,
+        handoffs=[],
+        tracing=ModelTracing.DISABLED,
+        previous_response_id=None,
+    )
+    assert "extra_headers" in called_kwargs
+    assert called_kwargs["extra_headers"]["X-Test-Header"] == "test-value"
+
+
+
+@pytest.mark.allow_call_model_methods
+@pytest.mark.asyncio
+async def test_extra_headers_passed_to_openai_client():
+    """
+    Ensure extra_headers in ModelSettings is passed to the OpenAI client.
+    """
+    called_kwargs = {}
+
+    class DummyCompletions:
+        async def create(self, **kwargs):
+            nonlocal called_kwargs
+            called_kwargs = kwargs
+            msg = ChatCompletionMessage(role="assistant", content="Hello")
+            choice = Choice(index=0, finish_reason="stop", message=msg)
+            return ChatCompletion(
+                id="resp-id",
+                created=0,
+                model="fake",
+                object="chat.completion",
+                choices=[choice],
+                usage=None,
+            )
+
+    class DummyClient:
+        def __init__(self):
+            self.chat = type("_Chat", (), {"completions": DummyCompletions()})()
+            self.base_url = "https://api.openai.com"
+
+    model = OpenAIChatCompletionsModel(model="gpt-4", openai_client=DummyClient()) # type: ignore
+    extra_headers = {"X-Test-Header": "test-value"}
+    await model.get_response(
+        system_instructions=None,
+        input="hi",
+        model_settings=ModelSettings(extra_headers=extra_headers),
+        tools=[],
+        output_schema=None,
+        handoffs=[],
+        tracing=ModelTracing.DISABLED,
+        previous_response_id=None,
+    )
+    assert "extra_headers" in called_kwargs
+    assert called_kwargs["extra_headers"]["X-Test-Header"] == "test-value"