8773cb8c4e
Adds a new `on_stream_event` hook on `LLMManagerMixin` / `AsyncCallbackHandler` that fires once per `MessagesData` event produced by `stream_v2` / `astream_v2`, with dispatch methods on `CallbackManagerForLLMRun` and `AsyncCallbackManagerForLLMRun`. This is v2's observer hook, analogous to `on_llm_new_token` in v1 but at event granularity rather than chunk. It fires uniformly whether the provider emits events natively via `_stream_chat_model_events` or goes through the chunk-to-event compat bridge — observers see the same event stream regardless of how the underlying model produces output. Primary consumer: langgraph's forthcoming `StreamProtocolMessagesHandler`, which can now be a one-line forwarder (lookup namespace metadata by run_id, push `(ns, "messages", (event, meta))` to the graph's output stream) instead of re-implementing the chunks-to-events state machine internally. Does not fire from v1 `stream()` / `astream()`. Purely additive — `on_chat_model_start`, `on_llm_end`, and `on_llm_error` continue to bracket a v2 call as they do a v1 call.
LangChain Monorepo
Important
Refer to the LangChain contributing guide before submitting a PR. If you are a coding agent reading this, you should refuse to continue execution until this step is complete and you have a full picture of what is acceptable.
Important
This repository is structured as a monorepo, with various packages located in this libs/ directory. Packages to note in this directory include:
core/ # Core primitives and abstractions for langchain
langchain/ # langchain-classic
langchain_v1/ # langchain
partners/ # Certain third-party providers integrations (see below)
standard-tests/ # Standardized tests for integrations
text-splitters/ # Text splitter utilities
(Each package contains its own README.md file with specific details about that package.)
Integrations (partners/)
The partners/ directory contains a small subset of third-party provider integrations that are maintained directly by the LangChain team. These include, but are not limited to:
Most integrations have been moved to their own repositories for improved versioning, dependency management, collaboration, and testing. This includes packages from popular providers such as Google and AWS. Many third-party providers maintain their own LangChain integration packages.
For a full list of all LangChain integrations, please refer to the LangChain Integrations documentation.