def on_llm_start(
        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,
        **kwargs: Any,
    ) -> Any:
        """Run when Chat Model starts running."""
        if context_api.get_value(_SUPPRESS_INSTRUMENTATION_KEY):
            return

        name = self._get_name_from_callback(serialized, kwargs=kwargs)
        span = self._create_llm_span(
            run_id, parent_run_id, name, LLMRequestTypeValues.COMPLETION
        )
        _set_llm_request(span, serialized, prompts, kwargs, self.spans[run_id])
Run when Chat Model starts running.
packages/opentelemetry-instrumentation-langchain/opentelemetry/instrumentation/langchain/callback_handler.py