fix(responses): echo "auto" for a tool_choice the bridge cannot express instead of failing after the provider call

litellm/responses/litellm_completion_transformation/transformation.py

@@ -287,8 +287,10 @@ class LiteLLMCompletionResponsesConfig:
                 return ToolChoiceCustomParam(type="custom", name=custom_name)
             case _, {"type": "function", "function": {"name": str(function_name)}}:
                 return ToolChoiceFunctionParam(type="function", name=function_name)
-            case _, normalized:
-                return _RESPONSES_API_TOOL_CHOICE_ADAPTER.validate_python(normalized)
+            case _, "none" | "auto" | "required" as normalized:
+                return normalized
+            case _, _:
+                return "auto"
 
     @staticmethod
     def _should_drop_derived_web_search_options(model: str, custom_llm_provider: str | None) -> bool:

tests/test_litellm/responses/litellm_completion_transformation/test_litellm_completion_responses.py

@@ -1435,6 +1435,9 @@ class TestToolChoiceTransformation:
             ("required", "required"),
             ("none", "none"),
             (None, "auto"),
+            ("any", "auto"),
+            ("run_command", "auto"),
+            ({"name": "run_command"}, "auto"),
         ],
     )
     def test_transform_tool_choice_for_responses_api_response(
@@ -1478,6 +1481,29 @@ class TestToolChoiceTransformation:
 
         assert responses_api_response.tool_choice == {"type": "function", "name": "run_command"}
 
+    def test_non_streamed_response_with_unrecognized_tool_choice_echoes_auto(self) -> None:
+        chat_completion_response: Final = ModelResponse(
+            id="chatcmpl-unrecognized-tool-choice",
+            created=1748575031,
+            model="claude-haiku-4-5",
+            object="chat.completion",
+            choices=[
+                Choices(
+                    index=0,
+                    finish_reason="stop",
+                    message=Message(role="assistant", content="/Users/dev"),
+                )
+            ],
+        )
+
+        responses_api_response: Final = LiteLLMCompletionResponsesConfig.transform_chat_completion_response_to_responses_api_response(
+            request_input="Run the command pwd.",
+            responses_api_request={"tool_choice": "any"},
+            chat_completion_response=chat_completion_response,
+        )
+
+        assert responses_api_response.tool_choice == "auto"
+
 
 class TestContentTypeTransformation:
     """Test content type transformation from Responses API to Chat Completion format"""

tests/test_litellm/responses/litellm_completion_transformation/test_streaming_iterator_transformation.py

@@ -685,3 +685,23 @@ def test_streamed_named_tool_choice_is_echoed_in_responses_api_shape() -> None:
         {"type": "function", "name": "run_command"},
     ]
     assert any(getattr(event, "type", None) == "response.output_item.done" for event in events)
+
+
+def test_streamed_unrecognized_tool_choice_is_echoed_as_auto() -> None:
+    iterator: Final = LiteLLMCompletionStreamingIterator(
+        model="claude-haiku-4-5",
+        litellm_custom_stream_wrapper=_FakeStreamWrapper([_tool_call_chunk(finish_reason="tool_calls")]),
+        request_input="Run the command pwd.",
+        responses_api_request={
+            "tools": [{"type": "function", "name": "run_command", "parameters": {"type": "object"}}],
+            "tool_choice": "any",
+        },
+        custom_llm_provider="anthropic",
+        litellm_metadata={},
+    )
+
+    response_events: Final = [
+        event for event in iterator if getattr(event, "type", None) in RESPONSE_ID_EVENT_TYPES
+    ]
+
+    assert [event.response.tool_choice for event in response_events] == ["auto", "auto", "auto"]