Tool calling broken through run_stream() when using gpt-oss in Ollama.

[ggozad]

Initial Checks

• I confirm that I'm using the latest version of Pydantic AI
• I confirm that I searched for my issue in https://github.com/pydantic/pydantic-ai/issues before opening this issue

Description

Hey, and thank you for a wonderful framework!

Using the example code attached, I expect gpt-oss to handle the (pretty easy) tool calling, however the tool is never called. Tool calling seems to work fine using the qwen3 model.
Also, this seems to be a problem with run_stream but not run which works as expected.

gpt-oss outputs the following:

["[Request] Starting part 0: TextPart(content='')",
 '[Result] The model starting producing a final result (tool_name=None)']

Whereas qwen3 does the whole thing:

["[Request] Starting part 0: ThinkingPart(content='', id='content', "
 "provider_name='ollama')",
 "[Request] Starting part 1: ToolCallPart(tool_name='get_current_datetime', "
 "args='{}', tool_call_id='call_39tumgp8')",
 "[Tools] The LLM calls tool='get_current_datetime' with args={} "
 "(tool_call_id='call_39tumgp8')",
 "[Tools] Tool call 'call_39tumgp8' returned => "
 '2025-09-29T15:17:28.423696+00:00',
 "[Request] Starting part 0: ThinkingPart(content='', id='content', "
 "provider_name='ollama')",
 "[Request] Starting part 1: TextPart(content='The')",
 '[Result] The model starting producing a final result (tool_name=None)',
 '[Output] The current time is',
 '[Output] The current time is **3:1',
 '[Output] The current time is **3:17 PM on September',
 '[Output] The current time is **3:17 PM on September 29,',
 '[Output] The current time is **3:17 PM on September 29, 202',
 '[Output] The current time is **3:17 PM on September 29, 2025 in UTC**',
 '[Output] The current time is **3:17 PM on September 29, 2025 in UTC**. Let '
 'me know',
 '[Output] The current time is **3:17 PM on September 29, 2025 in UTC**. Let '
 'me know if you need the',
 '[Output] The current time is **3:17 PM on September 29, 2025 in UTC**. Let '
 'me know if you need the time in a different',
 '[Output] The current time is **3:17 PM on September 29, 2025 in UTC**. Let '
 'me know if you need the time in a different timezone!']

Example Code

import asyncio
import datetime
from collections.abc import AsyncIterable

from pydantic_ai import Agent
from pydantic_ai import RunContext
from pydantic_ai.messages import AgentStreamEvent
from pydantic_ai.messages import FinalResultEvent
from pydantic_ai.messages import FunctionToolCallEvent
from pydantic_ai.messages import FunctionToolResultEvent
from pydantic_ai.messages import PartDeltaEvent
from pydantic_ai.messages import PartStartEvent
from pydantic_ai.messages import TextPartDelta
from pydantic_ai.messages import ToolCallPartDelta
from pydantic_ai.models.openai import OpenAIChatModel
from pydantic_ai.providers.ollama import OllamaProvider


def get_current_datetime():
    """Returns the current datetime in ISO format"""
    return datetime.datetime.now(datetime.UTC).isoformat()


async def event_stream_handler(
    ctx: RunContext,
    event_stream: AsyncIterable[AgentStreamEvent],
):
    async for event in event_stream:
        if isinstance(event, PartStartEvent):
            output_messages.append(
                f"[Request] Starting part {event.index}: {event.part!r}"
            )
        elif isinstance(event, PartDeltaEvent):
            if isinstance(event.delta, TextPartDelta):
                output_messages.append(
                    f"[Request] Part {event.index} text delta: {event.delta.content_delta!r}"
                )
            elif isinstance(event.delta, ToolCallPartDelta):
                output_messages.append(
                    f"[Request] Part {event.index} args delta: {event.delta.args_delta}"
                )
        elif isinstance(event, FunctionToolCallEvent):
            output_messages.append(
                f"[Tools] The LLM calls tool={event.part.tool_name!r} with args={event.part.args} (tool_call_id={event.part.tool_call_id!r})"
            )
        elif isinstance(event, FunctionToolResultEvent):
            output_messages.append(
                f"[Tools] Tool call {event.tool_call_id!r} returned => {event.result.content}"
            )
        elif isinstance(event, FinalResultEvent):
            output_messages.append(
                f"[Result] The model starting producing a final result (tool_name={event.tool_name})"
            )


output_messages: list[str] = []


async def test():
    model = OpenAIChatModel(
        provider=OllamaProvider(
            base_url="http://localhost:11434/v1", api_key="dummy"
        ),
        model_name="gpt-oss",
    )
    agent = Agent(model=model, tools=[get_current_datetime])

    async with agent.run_stream(
        "what time is it?", event_stream_handler=event_stream_handler
    ) as res:
        async for message in res.stream_text():
            output_messages.append(f"[Output] {message}")


if __name__ == "__main__":
    asyncio.run(test())
    from pprint import pprint

    pprint(output_messages)

Python, Pydantic AI & LLM client version

python 3.12
pydantic-ai 1.0.10
Ollama 0.12.3

[chandru10chandru]

i will go through it

[DouweM]

@ggozad Thanks Yiorgis, fixed in #3035!

This (slightly modified) example:

import asyncio
import datetime
from collections.abc import AsyncIterable

from pydantic_ai import Agent, RunContext
from pydantic_ai.messages import (
    AgentStreamEvent,
    FinalResultEvent,
    FunctionToolCallEvent,
    FunctionToolResultEvent,
    PartDeltaEvent,
    PartStartEvent,
    TextPartDelta,
    ThinkingPartDelta,
    ToolCallPartDelta,
)
from pydantic_ai.models.openai import OpenAIChatModel
from pydantic_ai.providers.ollama import OllamaProvider


def get_current_datetime():
    """Returns the current datetime in ISO format"""
    return datetime.datetime.now(datetime.UTC).isoformat()


async def event_stream_handler(
    ctx: RunContext,
    event_stream: AsyncIterable[AgentStreamEvent],
):
    async for event in event_stream:
        if isinstance(event, PartStartEvent):
            print(f'[Request] Starting part {event.index}: {event.part!r}')
        elif isinstance(event, PartDeltaEvent):
            if isinstance(event.delta, TextPartDelta):
                print(f'[Request] Part {event.index} text delta: {event.delta.content_delta!r}')
            elif isinstance(event.delta, ToolCallPartDelta):
                print(f'[Request] Part {event.index} args delta: {event.delta.args_delta}')
            elif isinstance(event.delta, ThinkingPartDelta):
                print(f'[Request] Part {event.index} args delta: {event.delta.content_delta}')
        elif isinstance(event, FunctionToolCallEvent):
            print(
                f'[Tools] The LLM calls tool={event.part.tool_name!r} with args={event.part.args} (tool_call_id={event.part.tool_call_id!r})'
            )
        elif isinstance(event, FunctionToolResultEvent):
            print(f'[Tools] Tool call {event.tool_call_id!r} returned => {event.result.content}')
        elif isinstance(event, FinalResultEvent):
            print(f'[Result] The model starting producing a final result (tool_name={event.tool_name})')


async def test():
    model = OpenAIChatModel(
        provider=OllamaProvider(base_url='http://localhost:11434/v1', api_key='dummy'),
        model_name='gpt-oss:20b',
    )
    agent = Agent(model=model, tools=[get_current_datetime])

    async with agent.run_stream('what time is it?', event_stream_handler=event_stream_handler) as res:
        async for message in res.stream_text():
            print(f'[Output] {message}')


if __name__ == '__main__':
    asyncio.run(test())

Now gives the following output:

Request] Starting part 0: ThinkingPart(content='The', id='reasoning', provider_name='ollama')
[Request] Part 0 args delta:  user
[Request] Part 0 args delta:  asks
[Request] Part 0 args delta:  "
[Request] Part 0 args delta: what
[Request] Part 0 args delta:  time
[Request] Part 0 args delta:  is
[Request] Part 0 args delta:  it
[Request] Part 0 args delta: ?"
[Request] Part 0 args delta:  Need
[Request] Part 0 args delta:  to
[Request] Part 0 args delta:  fetch
[Request] Part 0 args delta:  current
[Request] Part 0 args delta:  datetime
[Request] Part 0 args delta:  using
[Request] Part 0 args delta:  tool
[Request] Part 0 args delta:  get
[Request] Part 0 args delta: _current
[Request] Part 0 args delta: _datetime
[Request] Part 0 args delta: .
[Request] Part 0 args delta:  In
[Request] Part 0 args delta:  the
[Request] Part 0 args delta:  conversation
[Request] Part 0 args delta: ,
[Request] Part 0 args delta:  we
[Request] Part 0 args delta:  have
[Request] Part 0 args delta:  to
[Request] Part 0 args delta:  call
[Request] Part 0 args delta:  that
[Request] Part 0 args delta:  function
[Request] Part 0 args delta: .
[Request] Starting part 1: ToolCallPart(tool_name='get_current_datetime', args='{}', tool_call_id='call_a10joo35')
[Tools] The LLM calls tool='get_current_datetime' with args={} (tool_call_id='call_a10joo35')
[Tools] Tool call 'call_a10joo35' returned => 2025-09-29T22:46:36.302238+00:00
[Request] Starting part 0: TextPart(content='The')
[Result] The model starting producing a final result (tool_name=None)
[Output] The
[Output] The current
[Output] The current date
[Output] The current date and
[Output] The current date and time
[Output] The current date and time is
[Output] The current date and time is **
[Output] The current date and time is **202
[Output] The current date and time is **2025
[Output] The current date and time is **2025‑
[Output] The current date and time is **2025‑09
[Output] The current date and time is **2025‑09‑
[Output] The current date and time is **2025‑09‑29
[Output] The current date and time is **2025‑09‑29 
[Output] The current date and time is **2025‑09‑29 22
[Output] The current date and time is **2025‑09‑29 22:
[Output] The current date and time is **2025‑09‑29 22:46
[Output] The current date and time is **2025‑09‑29 22:46:
[Output] The current date and time is **2025‑09‑29 22:46:36
[Output] The current date and time is **2025‑09‑29 22:46:36 UTC
[Output] The current date and time is **2025‑09‑29 22:46:36 UTC**
[Output] The current date and time is **2025‑09‑29 22:46:36 UTC**.

[ggozad]

Thank you @DouweM for a fast fix!