Python: [Bug]: Chat Completions streaming loses logprobs after null chunks

Description

A Chat Completions streaming chunk with choice.logprobs=None overwrites populated logprobs from an earlier chunk during final response aggregation. A terminal chunk with an empty delta is sufficient to reproduce this.

Expected: The final response retains the last populated logprobs object.

Actual: response.text is hello, but response.additional_properties["logprobs"] is None.

Code Sample

This uses a mocked provider/client and makes no service request.

import asyncio
from unittest.mock import AsyncMock, patch

from agent_framework import Message
from agent_framework_openai import OpenAIChatCompletionClient
from openai.types.chat.chat_completion_chunk import ChatCompletionChunk


class MockStream:
    async def __aenter__(self):
        return self

    async def __aexit__(self, *args):
        pass

    def __aiter__(self):
        async def chunks():
            populated = {"content": [{"token": "hello", "bytes": [104, 101, 108, 108, 111], "logprob": -0.1, "top_logprobs": []}]}
            for delta, logprobs, finish_reason in [({"content": "hello"}, populated, None), ({}, None, "stop")]:
                yield ChatCompletionChunk.model_validate({
                    "id": "example-stream",
                    "object": "chat.completion.chunk",
                    "created": 0,
                    "model": "test-model",
                    "choices": [{"index": 0, "delta": delta, "logprobs": logprobs, "finish_reason": finish_reason}],
                })
        return chunks()


async def main():
    client = OpenAIChatCompletionClient(api_key="test-key", model="test-model")
    with patch.object(client.client.chat.completions, "create", new=AsyncMock(return_value=MockStream())):
        response = await client.get_response(
            messages=[Message(role="user", contents=["test"])],
            options={"logprobs": True},
            stream=True,
        ).get_final_response()
    print(response.text, response.additional_properties.get("logprobs"))
    assert response.additional_properties.get("logprobs") is not None


asyncio.run(main())

Package Versions

Source checkout e9857bd75a21843803431a2e7dfa41ee9b017ac7: agent-framework-core 1.20.0, agent-framework-openai 1.15.0; OpenAI SDK 3.23.0.

Python Version

Python 3.12.12.

Additional Context

I will submit a focused fix with regression coverage for this behavior.

🤖 Automated triage reproduction notes (agent-authored — trust but verify)

Agent analysis

Repro: python/packages/openai/agent_framework_openai/_chat_completion_client.py::_get_metadata_from_chat_choice emits logprobs: None for a terminal streaming choice, and _parse_response_update_from_openai places it in update metadata. Use a mocked two-chunk stream containing populated logprobs with "hello", followed by an empty delta with null logprobs and finish_reason="stop", then call get_final_response() and observe that final logprobs are None.

Failing test: python/packages/openai/tests/openai/test_openai_chat_completion_client.py::test_streaming_final_response_preserves_logprobs_after_null_chunk
Files examined: python/packages/openai/agent_framework_openai/_chat_completion_client.py, python/packages/openai/tests/openai/test_openai_chat_completion_client.py, python/packages/core/agent_framework/_clients.py, python/packages/core/agent_framework/_types.py, python/packages/openai/pyproject.toml
Tests run: test_streaming_final_response_preserves_logprobs_after_null_chunk, test_streaming_closes_provider_stream_on_completion
Reported version: agent-framework-openai 1.15.0
Current version: agent-framework-openai 1.15.0

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Python: [Bug]: Chat Completions streaming loses logprobs after null chunks #8996

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Python: [Bug]: Chat Completions streaming loses logprobs after null chunks #8996

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github-actions commented on Oct 3, 2026

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