Export user_agent_override contextmanager

src/agents/extensions/models/litellm_model.py

@@ -39,7 +39,7 @@
 from ...logger import logger
 from ...model_settings import ModelSettings
 from ...models.chatcmpl_converter import Converter
-from ...models.chatcmpl_helpers import HEADERS
+from ...models.chatcmpl_helpers import HEADERS, USER_AGENT_OVERRIDE
 from ...models.chatcmpl_stream_handler import ChatCmplStreamHandler
 from ...models.fake_id import FAKE_RESPONSES_ID
 from ...models.interface import Model, ModelTracing
@@ -353,7 +353,7 @@ async def _fetch_response(
             stream_options=stream_options,
             reasoning_effort=reasoning_effort,
             top_logprobs=model_settings.top_logprobs,
-            extra_headers={**HEADERS, **(model_settings.extra_headers or {})},
+            extra_headers=self._merge_headers(model_settings),
             api_key=self.api_key,
             base_url=self.base_url,
             **extra_kwargs,
@@ -384,6 +384,13 @@ def _remove_not_given(self, value: Any) -> Any:
             return None
         return value
 
+    def _merge_headers(self, model_settings: ModelSettings):
+        merged = {**HEADERS, **(model_settings.extra_headers or {})}
+        ua_ctx = USER_AGENT_OVERRIDE.get()
+        if ua_ctx is not None:
+            merged["User-Agent"] = ua_ctx
+        return merged
+
 
 class LitellmConverter:
     @classmethod

src/agents/models/chatcmpl_helpers.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from contextvars import ContextVar
+
 from openai import AsyncOpenAI
 
 from ..model_settings import ModelSettings
@@ -8,6 +10,10 @@
 _USER_AGENT = f"Agents/Python {__version__}"
 HEADERS = {"User-Agent": _USER_AGENT}
 
+USER_AGENT_OVERRIDE: ContextVar[str | None] = ContextVar(
+    "openai_chatcompletions_user_agent_override", default=None
+)
+
 
 class ChatCmplHelpers:
     @classmethod

src/agents/models/openai_chatcompletions.py

@@ -25,7 +25,7 @@
 from ..usage import Usage
 from ..util._json import _to_dump_compatible
 from .chatcmpl_converter import Converter
-from .chatcmpl_helpers import HEADERS, ChatCmplHelpers
+from .chatcmpl_helpers import HEADERS, USER_AGENT_OVERRIDE, ChatCmplHelpers
 from .chatcmpl_stream_handler import ChatCmplStreamHandler
 from .fake_id import FAKE_RESPONSES_ID
 from .interface import Model, ModelTracing
@@ -306,7 +306,7 @@ async def _fetch_response(
             reasoning_effort=self._non_null_or_not_given(reasoning_effort),
             verbosity=self._non_null_or_not_given(model_settings.verbosity),
             top_logprobs=self._non_null_or_not_given(model_settings.top_logprobs),
-            extra_headers={**HEADERS, **(model_settings.extra_headers or {})},
+            extra_headers=self._merge_headers(model_settings),
             extra_query=model_settings.extra_query,
             extra_body=model_settings.extra_body,
             metadata=self._non_null_or_not_given(model_settings.metadata),
@@ -349,3 +349,10 @@ def _get_client(self) -> AsyncOpenAI:
         if self._client is None:
             self._client = AsyncOpenAI()
         return self._client
+
+    def _merge_headers(self, model_settings: ModelSettings):
+        merged = {**HEADERS, **(model_settings.extra_headers or {})}
+        ua_ctx = USER_AGENT_OVERRIDE.get()
+        if ua_ctx is not None:
+            merged["User-Agent"] = ua_ctx
+        return merged

src/agents/models/openai_responses.py

@@ -2,6 +2,7 @@
 
 import json
 from collections.abc import AsyncIterator
+from contextvars import ContextVar
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, Any, Literal, cast, overload
 
@@ -49,6 +50,11 @@
 _USER_AGENT = f"Agents/Python {__version__}"
 _HEADERS = {"User-Agent": _USER_AGENT}
 
+# Override for the User-Agent header used by the Responses API.
+_USER_AGENT_OVERRIDE: ContextVar[str | None] = ContextVar(
+    "openai_responses_user_agent_override", default=None
+)
+
 
 class OpenAIResponsesModel(Model):
     """
@@ -312,7 +318,7 @@ async def _fetch_response(
             tool_choice=tool_choice,
             parallel_tool_calls=parallel_tool_calls,
             stream=stream,
-            extra_headers={**_HEADERS, **(model_settings.extra_headers or {})},
+            extra_headers=self._merge_headers(model_settings),
             extra_query=model_settings.extra_query,
             extra_body=model_settings.extra_body,
             text=response_format,
@@ -327,6 +333,13 @@ def _get_client(self) -> AsyncOpenAI:
             self._client = AsyncOpenAI()
         return self._client
 
+    def _merge_headers(self, model_settings: ModelSettings):
+        merged = {**_HEADERS, **(model_settings.extra_headers or {})}
+        ua_ctx = _USER_AGENT_OVERRIDE.get()
+        if ua_ctx is not None:
+            merged["User-Agent"] = ua_ctx
+        return merged
+
 
 @dataclass
 class ConvertedTools:

tests/models/test_litellm_user_agent.py

@@ -0,0 +1,89 @@
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+
+from agents import ModelSettings, ModelTracing, __version__
+from agents.models.chatcmpl_helpers import USER_AGENT_OVERRIDE
+
+
+@pytest.mark.allow_call_model_methods
+@pytest.mark.asyncio
+@pytest.mark.parametrize("override_ua", [None, "test_user_agent"])
+async def test_user_agent_header_litellm(override_ua: str | None, monkeypatch):
+    called_kwargs: dict[str, Any] = {}
+    expected_ua = override_ua or f"Agents/Python {__version__}"
+
+    import importlib
+    import sys
+    import types as pytypes
+
+    litellm_fake: Any = pytypes.ModuleType("litellm")
+
+    class DummyMessage:
+        role = "assistant"
+        content = "Hello"
+        tool_calls: list[Any] | None = None
+
+        def get(self, _key, _default=None):
+            return None
+
+        def model_dump(self):
+            return {"role": self.role, "content": self.content}
+
+    class Choices:  # noqa: N801 - mimic litellm naming
+        def __init__(self):
+            self.message = DummyMessage()
+
+    class DummyModelResponse:
+        def __init__(self):
+            self.choices = [Choices()]
+
+    async def acompletion(**kwargs):
+        nonlocal called_kwargs
+        called_kwargs = kwargs
+        return DummyModelResponse()
+
+    utils_ns = pytypes.SimpleNamespace()
+    utils_ns.Choices = Choices
+    utils_ns.ModelResponse = DummyModelResponse
+
+    litellm_types = pytypes.SimpleNamespace(
+        utils=utils_ns,
+        llms=pytypes.SimpleNamespace(openai=pytypes.SimpleNamespace(ChatCompletionAnnotation=dict)),
+    )
+    litellm_fake.acompletion = acompletion
+    litellm_fake.types = litellm_types
+
+    monkeypatch.setitem(sys.modules, "litellm", litellm_fake)
+
+    litellm_mod = importlib.import_module("agents.extensions.models.litellm_model")
+    monkeypatch.setattr(litellm_mod, "litellm", litellm_fake, raising=True)
+    LitellmModel = litellm_mod.LitellmModel
+
+    model = LitellmModel(model="gpt-4")
+
+    if override_ua is not None:
+        token = USER_AGENT_OVERRIDE.set(override_ua)
+    else:
+        token = None
+    try:
+        await model.get_response(
+            system_instructions=None,
+            input="hi",
+            model_settings=ModelSettings(),
+            tools=[],
+            output_schema=None,
+            handoffs=[],
+            tracing=ModelTracing.DISABLED,
+            previous_response_id=None,
+            conversation_id=None,
+            prompt=None,
+        )
+    finally:
+        if token is not None:
+            USER_AGENT_OVERRIDE.reset(token)
+
+    assert "extra_headers" in called_kwargs
+    assert called_kwargs["extra_headers"]["User-Agent"] == expected_ua

tests/test_openai_chatcompletions.py

@@ -31,9 +31,10 @@
     ModelTracing,
     OpenAIChatCompletionsModel,
     OpenAIProvider,
+    __version__,
     generation_span,
 )
-from agents.models.chatcmpl_helpers import ChatCmplHelpers
+from agents.models.chatcmpl_helpers import USER_AGENT_OVERRIDE, ChatCmplHelpers
 from agents.models.fake_id import FAKE_RESPONSES_ID
 
 
@@ -370,6 +371,60 @@ def test_store_param():
         "Should respect explicitly set store=True"
     )
 
+
+@pytest.mark.allow_call_model_methods
+@pytest.mark.asyncio
+@pytest.mark.parametrize("override_ua", [None, "test_user_agent"])
+async def test_user_agent_header_chat_completions(override_ua):
+    called_kwargs: dict[str, Any] = {}
+    expected_ua = override_ua or f"Agents/Python {__version__}"
+
+    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 DummyChatClient:
+        def __init__(self):
+            self.chat = type("_Chat", (), {"completions": DummyCompletions()})()
+            self.base_url = "https://api.openai.com"
+
+    model = OpenAIChatCompletionsModel(model="gpt-4", openai_client=DummyChatClient())  # type: ignore
+
+    if override_ua is not None:
+        token = USER_AGENT_OVERRIDE.set(override_ua)
+    else:
+        token = None
+
+    try:
+        await model.get_response(
+            system_instructions=None,
+            input="hi",
+            model_settings=ModelSettings(),
+            tools=[],
+            output_schema=None,
+            handoffs=[],
+            tracing=ModelTracing.DISABLED,
+            previous_response_id=None,
+            conversation_id=None,
+        )
+    finally:
+        if token is not None:
+            USER_AGENT_OVERRIDE.reset(token)
+
+    assert "extra_headers" in called_kwargs
+    assert called_kwargs["extra_headers"]["User-Agent"] == expected_ua
+
     client = AsyncOpenAI(base_url="http://www.notopenai.com")
     model_settings = ModelSettings()
     assert ChatCmplHelpers.get_store_param(client, model_settings) is None, (

tests/test_openai_responses.py

@@ -0,0 +1,65 @@
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+from openai.types.responses import ResponseCompletedEvent
+
+from agents import ModelSettings, ModelTracing, __version__
+from agents.models.openai_responses import _USER_AGENT_OVERRIDE as RESP_UA, OpenAIResponsesModel
+from tests.fake_model import get_response_obj
+
+
+@pytest.mark.allow_call_model_methods
+@pytest.mark.asyncio
+@pytest.mark.parametrize("override_ua", [None, "test_user_agent"])
+async def test_user_agent_header_responses(override_ua: str | None):
+    called_kwargs: dict[str, Any] = {}
+    expected_ua = override_ua or f"Agents/Python {__version__}"
+
+    class DummyStream:
+        def __aiter__(self):
+            async def gen():
+                yield ResponseCompletedEvent(
+                    type="response.completed",
+                    response=get_response_obj([]),
+                    sequence_number=0,
+                )
+
+            return gen()
+
+    class DummyResponses:
+        async def create(self, **kwargs):
+            nonlocal called_kwargs
+            called_kwargs = kwargs
+            return DummyStream()
+
+    class DummyResponsesClient:
+        def __init__(self):
+            self.responses = DummyResponses()
+
+    model = OpenAIResponsesModel(model="gpt-4", openai_client=DummyResponsesClient())  # type: ignore
+
+    if override_ua is not None:
+        token = RESP_UA.set(override_ua)
+    else:
+        token = None
+
+    try:
+        stream = model.stream_response(
+            system_instructions=None,
+            input="hi",
+            model_settings=ModelSettings(),
+            tools=[],
+            output_schema=None,
+            handoffs=[],
+            tracing=ModelTracing.DISABLED,
+        )
+        async for _ in stream:
+            pass
+    finally:
+        if token is not None:
+            RESP_UA.reset(token)
+
+    assert "extra_headers" in called_kwargs
+    assert called_kwargs["extra_headers"]["User-Agent"] == expected_ua