self,
        serialized: Dict[str, Any],
        prompts: List[str],
        *,
        run_id: UUID,
        tags: Optional[List[str]] = None,
        parent_run_id: Optional[UUID] = None,
        metadata: Optional[Dict[str, Any]] = None,
        name: Optional[str] = None,
        **kwargs: Any,
    ) -> Run:
        """Start a trace for an LLM run."""
        parent_run_id_ = str(parent_run_id) if parent_run_id else None
        execution_order = self._get_execution_order(parent_run_id_)
        start_time = datetime.utcnow()
        if metadata:
            kwargs.update({"metadata": metadata})
        llm_run = Run(
            id=run_id,
            parent_run_id=parent_run_id,
            serialized=serialized,
            inputs={"prompts": prompts},
            extra=kwargs,
            events=[{"name": "start", "time": start_time}],
            start_time=start_time,
            execution_order=execution_order,
            child_execution_order=execution_order,
            run_type="llm",
            tags=tags or [],
            name=name,
        )
        self._start_trace(llm_run)
        self._on_llm_start(llm_run)
        return llm_run
[docs]    def on_llm_new_token(
        self,
        token: str,
        *,
        chunk: Optional[Union[GenerationChunk, ChatGenerationChunk]] = None,
        run_id: UUID,
        parent_run_id: Optional[UUID] = None,
        **kwargs: Any,
    ) -> Run:
        """Run on new LLM token. Only available when streaming is enabled."""
        if not run_id: