<path_to_project>.venv\Scripts\python.exe <path_to_project>\langchain_test.py Traceback (most recent call last): File "<path_to_project>\langchain_test.py", line 33, in <module> asyncio.run(main()) File "C:\Python312\Lib\asyncio\runners.py", line 195, in run return runner.run(main) ^^^^^^^^^^^^^^^^ File "C:\Python312\Lib\asyncio\runners.py", line 118, in run return self._loop.run_until_complete(task) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "C:\Python312\Lib\asyncio\base_events.py", line 691, in run_until_complete return future.result() ^^^^^^^^^^^^^^^ File "<path_to_project>\langchain_test.py", line 27, in main result = await agent.ainvoke({"messages": [{"role": "user", "content": "What's the weather like in New York?"}]}) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langgraph\pregel\main.py", line 3462, in ainvoke async for chunk in self.astream( File "<path_to_project>.venv\Lib\site-packages\langgraph\pregel\main.py", line 3111, in astream async for _ in runner.atick( File "<path_to_project>.venv\Lib\site-packages\langgraph\pregel_runner.py", line 304, in atick await arun_with_retry( File "<path_to_project>.venv\Lib\site-packages\langgraph\pregel_retry.py", line 211, in arun_with_retry return await task.proc.ainvoke(task.input, config) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langgraph_internal_runnable.py", line 705, in ainvoke input = await asyncio.create_task( ^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langgraph_internal_runnable.py", line 473, in ainvoke ret = await self.afunc(*args, **kwargs) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langchain\agents\factory.py", line 1349, in amodel_node model_response = await _execute_model_async(request) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langchain\agents\factory.py", line 1321, in execute_model_async output = await model.ainvoke(messages) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langchain_core\runnables\base.py", line 5708, in ainvoke return await self.bound.ainvoke( ^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langchain_core\language_models\chat_models.py", line 477, in ainvoke llm_result = await self.agenerate_prompt( ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langchain_core\language_models\chat_models.py", line 1212, in agenerate_prompt return await self.agenerate( ^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langchain_core\language_models\chat_models.py", line 1170, in agenerate raise exceptions[0] File "<path_to_project>.venv\Lib\site-packages\langchain_core\language_models\chat_models.py", line 1439, in _agenerate_with_cache result = await self._agenerate( ^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\langchain_openai\chat_models\base.py", line 1752, in _agenerate _handle_openai_bad_request(e) File "<path_to_project>.venv\Lib\site-packages\langchain_openai\chat_models\base.py", line 1733, in _agenerate await self.root_async_client.responses.with_raw_response.create( File "<path_to_project>.venv\Lib\site-packages\openai_legacy_response.py", line 384, in wrapped return cast(LegacyAPIResponse[R], await func(*args, **kwargs)) ^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\openai\resources\responses\responses.py", line 2565, in create return await self._post( ^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\openai_base_client.py", line 1884, in post return await self.request(cast_to, opts, stream=stream, stream_cls=stream_cls) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "<path_to_project>.venv\Lib\site-packages\openai_base_client.py", line 1669, in request raise self._make_status_error_from_response(err.response) from None openai.BadRequestError: Error code: 400 - {'error': {'message': 'input[4]: json: cannot unmarshal array into Go struct field ResponsesFunctionCallOutput.output of type string', 'type': 'invalid_request_error', 'param': None, 'code': None}} During task with name 'model' and id '498551a6-76c1-3791-aa56-3650278b531f'

Fix Plan

The issue seems to be related to the compatibility between MultiServerMCPClient and ChatOpenai with configured reasoning. To fix this, we can try the following steps:

• Update the langchain_openai package to the latest version.
• Check the reasoning configuration in ChatOpenai and make sure it is compatible with MultiServerMCPClient.
• Try removing the reasoning configuration or setting it to a default value.

Here is an example of how to update the reasoning configuration:

chat = ChatOpenAI(
    base_url="http://localhost:11434/v1",
    api_key="blank",
    model="qwen3.5:4b",
    reasoning={"effort": "default"}  # or remove this line to use default reasoning
)

Alternatively, you can try using a different Chat model that is compatible with MultiServerMCPClient, such as ChatOllama.

Verification

To verify that the fix worked, you can run the same code again and check if the agent invocation is successful. You can also add some debug logging to see if the reasoning configuration is being applied correctly.

Extra Tips

• Make sure to check the documentation for langchain_openai and MultiServerMCPClient to see if there are any known issues or compatibility problems.
• If you are still experiencing issues, try to isolate the problem by removing other components or configurations and see if the issue persists.
• Consider opening an issue on the langchain GitHub repository if you are unable to resolve the issue on your own.