deepseek tool calls `reasoning_content` support

[CFITCorporation]

Description

https://api-docs.deepseek.com/guides/thinking_mode
"Since the tool invocation process in thinking mode requires users to pass back reasoning_content to the API, if your code does not correctly pass back reasoning_content, the API will return a 400 error. Please refer to the sample code below for the correct way."

Request for adding items reasoning_content to pydantic-ai(message_history mode)

References

No response

[dsfaccini]

hey @CFITCorporation thank you for the info. I'm working on this PR to support raw reasoning #3559 so I could include this, but ti would be helpful if you can provide the code you're using to trigger the error before I do. Could you do that?

[CFITCorporation]

the code below works before Dec. unitl DeepSeek's Upgrade.
DeepSeek updated its DeepSeek-V3.2 Release on 2025/12/1 so sth may be change

# config_trigger.py
API_KEY = 'sk-REPLACE_IT_WITH_REAL_API_KEY' # Replace it with real api key!!
DS_BASE_URL = 'https://api.deepseek.com'
DS_MODEL = 'deepseek-reasoner'
SYSTEM_PROMPT = """You are a helpful assistant."""

# trigger.py
from pydantic_ai import Agent
from pydantic_ai.models.openai import OpenAIModel
from pydantic_ai.providers.openai import OpenAIProvider
from config_trigger import API_KEY, DS_BASE_URL, DS_MODEL, SYSTEM_PROMPT
from datetime import datetime
from typing import Dict
def getTime() -> Dict[str, str]:
    return {"time":str(datetime.now())}
deepseek_provider = OpenAIProvider(
    base_url=DS_BASE_URL, 
    api_key=API_KEY
)
model = OpenAIModel(
    DS_MODEL,
    provider=deepseek_provider
)
agent = Agent(
    model=model,
    system_prompt=SYSTEM_PROMPT,
    tools=[
        getTime
    ]
)
result = agent.run_sync("What's the time?")
print(result.output)

Error log:

Traceback (most recent call last):
  File "C:\Users\cfittop\AppData\Roaming\Python\Python311\site-packages\pydantic_ai\models\openai.py", line 499, in _completions_create
    return await self.client.chat.completions.create(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\openai\resources\chat\completions\completions.py", line 2603, in create
    return await self._post(
           ^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\openai\_base_client.py", line 1794, in post
    return await self.request(cast_to, opts, stream=stream, stream_cls=stream_cls)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\openai\_base_client.py", line 1594, in request
    raise self._make_status_error_from_response(err.response) from None
openai.BadRequestError: Error code: 400 - {'error': {'message': 'Missing `reasoning_content` field in the assistant message at message index 2. For more information, please refer to https://api-docs.deepseek.com/guides/thinking_mode#tool-calls', 'type': 'invalid_request_error', 'param': None, 'code': 'invalid_request_error'}}

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "E:\jsFile\projectagent\trigger.py", line 28, in <module>
    result = agent.run_sync("What's the time?")
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Roaming\Python\Python311\site-packages\pydantic_ai\agent\abstract.py", line 337, in run_sync
    return _utils.get_event_loop().run_until_complete(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 653, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Roaming\Python\Python311\site-packages\pydantic_ai\agent\abstract.py", line 234, in run
    async for node in agent_run:
  File "C:\Users\cfittop\AppData\Roaming\Python\Python311\site-packages\pydantic_ai\run.py", line 148, in __anext__
    task = await anext(self._graph_run)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\pydantic_graph\beta\graph.py", line 410, in __anext__
    self._next = await self._iterator.asend(self._next)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\pydantic_graph\beta\graph.py", line 497, in iter_graph
    with _unwrap_exception_groups():
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\contextlib.py", line 155, in __exit__
    self.gen.throw(typ, value, traceback)
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\pydantic_graph\beta\graph.py", line 866, in _unwrap_exception_groups
    raise exception
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\pydantic_graph\beta\graph.py", line 638, in _run_tracked_task
    result = await self._run_task(t_)
             ^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\pydantic_graph\beta\graph.py", line 667, in _run_task
    output = await node.call(step_context)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Local\Programs\Python\Python311\Lib\site-packages\pydantic_graph\beta\step.py", line 253, in _call_node
    return await node.run(GraphRunContext(state=ctx.state, deps=ctx.deps))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Roaming\Python\Python311\site-packages\pydantic_ai\_agent_graph.py", line 420, in run
    return await self._make_request(ctx)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Roaming\Python\Python311\site-packages\pydantic_ai\_agent_graph.py", line 462, in _make_request
    model_response = await ctx.deps.model.request(message_history, model_settings, model_request_parameters)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Roaming\Python\Python311\site-packages\pydantic_ai\models\openai.py", line 417, in request
    response = await self._completions_create(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\cfittop\AppData\Roaming\Python\Python311\site-packages\pydantic_ai\models\openai.py", line 529, in _completions_create
    raise ModelHTTPError(status_code=status_code, model_name=self.model_name, body=e.body) from e
pydantic_ai.exceptions.ModelHTTPError: status_code: 400, model_name: deepseek-reasoner, body: {'message': 'Missing `reasoning_content` field in the assistant message at message index 2. For more information, please refer to https://api-docs.deepseek.com/guides/thinking_mode#tool-calls', 'type': 'invalid_request_error', 'param': None, 'code': 'invalid_request_error'}

while replace DS_MODEL = 'deepseek-reasoner' with DS_MODEL = 'deepseek-chat',it works normally.

# DS_MODEL = 'deepseek-chat'
The current time is December 5, 2025 at 1:30:42 AM.

thx!

[DouweM]

This was already fixed in #3536 and released 2 days ago, just make sure you're using the DeepSeekProvider: https://ai.pydantic.dev/models/openai/#deepseek