arguments in tool_called streaming event with 0.2.10

[nasirus]

Summary

When using Runner.run_streamed() with tool calls, the arguments field in event.item.raw_item.arguments is empty during streaming events, despite the tool function receiving the correct arguments and executing properly.

Bug Description

In streaming mode, accessing tool call arguments through event.item.raw_item.arguments returns an empty string, while the actual tool function receives and processes the arguments correctly. This creates inconsistent behavior between what's visible in the stream events and what's actually passed to the tool.

Steps to Reproduce

1. Create a simple agent with a tool that takes structured arguments
2. Use Runner.run_streamed() to execute a query that triggers the tool
3. Inspect the arguments field in streaming events of type tool_call_item

Minimal Reproduction Code

import asyncio
from agents import Agent, Runner, function_tool
from pydantic import BaseModel

class Location(BaseModel):
    lat: float
    long: float

@function_tool
async def fetch_weather(location: Location) -> str:
    """Fetch the weather for a given location.
    
    Args:
        location: The location to fetch the weather for.
    """
    print(f"Arguments from inside the function: {location.model_dump_json()}")
    return "sunny"

async def main():
    agent = Agent(
        name="Weather Agent",
        instructions="You are a helpful assistant.",
        tools=[fetch_weather],
    )
    
    result = Runner.run_streamed(agent, input="what is the weather in Tokyo?")
    async for event in result.stream_events():
        if event.type == "run_item_stream_event":
            if event.item.type == "tool_call_item":
                print(f"Tool call: {event.item.raw_item.name}")
                print(f"Arguments from outside the function: {event.item.raw_item.arguments}")

if __name__ == "__main__":
    asyncio.run(main())

Expected Behavior

The event.item.raw_item.arguments should contain the JSON string of the arguments being passed to the tool function, such as:

Arguments from outside the function: {"lat":35.6895,"long":139.6917}

Actual Behavior

The event.item.raw_item.arguments is empty:

Tool call: fetch_weather
Arguments from outside the function: 
Arguments from inside the function: {"lat":35.6895,"long":139.6917}

Environment Details

• OpenAI Agents SDK version: 0.2.10
• Python version: 3.12.0
• Operating System: Windows

[ahouse73]

Reproduced it in version 0.2.10, but not in 0.2.4, so was introduced in this time.

[nasirus]

It was working for me on 0.2.6.

[seratch]

Thanks for reporting this issue. I've confirmed this behavioral change starting in version 0.2.10. If this is critical for your apps, please use 0.2.9 for the time being.

The direct cause is #1300; the tool_called event needs to be submitted after collecting the delta data from response.function_call_arguments.delta events. @habema I will look into this later, but do you have any ideas to resolve this?

[habema]

Just PR'd a fix.

The issue was that tool_called events were being emitted on ResponseOutputItemAddedEvent (which has empty arguments) instead of ResponseOutputItemDoneEvent (which has complete arguments).

I also added some tests to make sure this doesn't happen again.

Check #1636

[nasirus]

Thank you everybody for your quick response.