feat(anthropic): add User-Agent header for Anthropic API calls (#35268)

libs/partners/anthropic/langchain_anthropic/chat_models.py

@@ -57,6 +57,7 @@ from langchain_core.utils.utils import _build_model_kwargs
 from pydantic import BaseModel, ConfigDict, Field, SecretStr, model_validator
 from typing_extensions import NotRequired, Self, TypedDict
 
+from langchain_anthropic import __version__
 from langchain_anthropic._client_utils import (
     _get_default_async_httpx_client,
     _get_default_httpx_client,
@@ -74,6 +75,8 @@ _message_type_lookups = {
 
 _MODEL_PROFILES = cast(ModelProfileRegistry, _PROFILES)
 
+_USER_AGENT: Final[str] = f"langchain-anthropic/{__version__}"
+
 
 def _get_default_model_profile(model_name: str) -> ModelProfile:
     """Get the default profile for a model.
@@ -1025,11 +1028,16 @@ class ChatAnthropic(BaseChatModel):
 
     @cached_property
     def _client_params(self) -> dict[str, Any]:
+        # Merge User-Agent with user-provided headers (user headers take precedence)
+        default_headers = {"User-Agent": _USER_AGENT}
+        if self.default_headers:
+            default_headers.update(self.default_headers)
+
         client_params: dict[str, Any] = {
             "api_key": self.anthropic_api_key.get_secret_value(),
             "base_url": self.anthropic_api_url,
             "max_retries": self.max_retries,
-            "default_headers": (self.default_headers or None),
+            "default_headers": default_headers,
         }
         # value <= 0 indicates the param should be ignored. None is a meaningful value
         # for Anthropic client and treated differently than not specifying the param at

libs/partners/anthropic/tests/unit_tests/test_chat_models.py

@@ -53,6 +53,15 @@ def test_initialization() -> None:
         assert model.anthropic_api_url == "https://api.anthropic.com"
 
 
+def test_user_agent_header_in_client_params() -> None:
+    """Test that _client_params includes a User-Agent header."""
+    llm = ChatAnthropic(model=MODEL_NAME, api_key="test-key")  # type: ignore[arg-type]
+    params = llm._client_params
+    assert "default_headers" in params
+    assert "User-Agent" in params["default_headers"]
+    assert params["default_headers"]["User-Agent"].startswith("langchain-anthropic/")
+
+
 @pytest.mark.parametrize("async_api", [True, False])
 def test_streaming_attribute_should_stream(async_api: bool) -> None:  # noqa: FBT001
     llm = ChatAnthropic(model=MODEL_NAME, streaming=True)