fix(core): include llm_output in streaming LLMResult

[zhangzhefang-github]

Summary

Fixes #34057 - Ensures that streaming mode includes llm_output field in LLMResult, fixing broken callback integrations.

Description

Previously, when using streaming mode (stream() or astream()), the LLMResult passed to on_llm_end callbacks was missing the llm_output field. This caused issues for callback handlers like Langfuse that rely on this field to extract metadata such as model names.

This PR adds llm_output={} to all streaming on_llm_end calls in both BaseLLM and BaseChatModel, ensuring consistency with non-streaming behavior.

Changes

• Updated BaseLLM.stream() to include llm_output={} in LLMResult
• Updated BaseLLM.astream() to include llm_output={} in LLMResult
• Updated BaseChatModel.stream() to include llm_output={} in LLMResult
• Updated BaseChatModel.astream() to include llm_output={} in LLMResult
• Added unit test test_stream_llm_result_contains_llm_output() to verify the fix

Test Plan

• ✅ All existing tests pass
• ✅ New test verifies llm_output field is present and is a dict in streaming mode
• ✅ Tested with GenericFakeChatModel using callback handler

[codspeed-hq]

CodSpeed Performance Report

Merging #34060 will not alter performance

_{Comparing zhangzhefang-github:fix/streaming-llm-output (b2abc0d) with master (525d5c0)¹}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched
⏩ 21 skipped²

Footnotes

1. No successful run was found on master (ee3373a) during the generation of this report, so 525d5c0 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 21 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩