langchain/callbacks/streaming_stdout_final_only.py/FinalStreamingStdOutCallbackHandler/on_llm_start
class FinalStreamingStdOutCallbackHandler:    def on_llm_start(
        self, serialized: Dict[str, Any], prompts: List[str], **kwargs: Any
    ) -> None:
        """Run when LLM starts running."""
        self.answer_reached = False