Migrating to Astream Events v2

danger

This migration guide is a work in progress and is not complete. Please wait to migrate astream_events.

We've added a v2 of the astream_events API with the release of 0.2.0. You can see this PR for more details.

The v2 version is a re-write of the v1 version, and should be more efficient, with more consistent output for the events. The v1 version of the API will be deprecated in favor of the v2 version and will be removed in 0.4.0.

Below is a list of changes between the v1 and v2 versions of the API.

output for on_chat_model_end

In v1, the outputs associated with on_chat_model_end changed depending on whether the chat model was run as a root level runnable or as part of a chain.

As a root level runnable the output was:

"data": {"output": AIMessageChunk(content="hello world!", id='some id')}

As part of a chain the output was:

            "data": {
                "output": {
                    "generations": [
                        [
                            {
                                "generation_info": None,
                                "message": AIMessageChunk(
                                    content="hello world!", id=AnyStr()
                                ),
                                "text": "hello world!",
                                "type": "ChatGenerationChunk",
                            }
                        ]
                    ],
                    "llm_output": None,
                }
            },

As of v2, the output will always be the simpler representation:

"data": {"output": AIMessageChunk(content="hello world!", id='some id')}

note

Non chat models (i.e., regular LLMs) are will be consistently associated with the more verbose format for now.

output for on_retriever_end

on_retriever_end output will always return a list of Documents.

Before:

{
    "data": {
        "output": [
            Document(...),
            Document(...),
            ...
        ]
    }
}

Removed on_retriever_stream

The on_retriever_stream event was an artifact of the implementation and has been removed.

Full information associated with the event is already available in the on_retriever_end event.

Please use on_retriever_end instead.

Removed on_tool_stream

The on_tool_stream event was an artifact of the implementation and has been removed.

Full information associated with the event is already available in the on_tool_end event.

Please use on_tool_end instead.

Propagating Names

Names of runnables have been updated to be more consistent.

model = GenericFakeChatModel(messages=infinite_cycle).configurable_fields(
    messages=ConfigurableField(
        id="messages",
        name="Messages",
        description="Messages return by the LLM",
    )
)

In v1, the event name was RunnableConfigurableFields.

In v2, the event name is GenericFakeChatModel.

If you're filtering by event names, check if you need to update your filters.

RunnableRetry

Usage of RunnableRetry within an LCEL chain being streamed generated an incorrect on_chain_end event in v1 corresponding to the failed runnable invocation that was being retried. This event has been removed in v2.

No action is required for this change.