LangGraph is an open-source agent runtime and low-level orchestration framework from LangChain. It lets developers' agents handle complex, long-running tasks reliably by giving precise control over how an agent reasons, calls tools and moves between steps, while still letting it act on its own.

Key features:

Design single-agent, multi-agent and hierarchical control flows with low-level graph primitives.
Add human-in-the-loop checks to moderate, steer and approve agent actions.
Persist memory so conversation history and state carry across sessions.
Stream tokens and intermediate steps to show agent reasoning in real time.
Use any model provider, with high-level abstractions or fine-grained control.
Debug and deploy agents through LangSmith Studio and LangSmith Deployment.

LangGraph is available for Python and JavaScript under the MIT license and can run on any infrastructure. Hosted deployment goes through LangSmith, whose free Developer plan has no deployments and whose Plus plan ($39 per seat a month, then pay as you go) includes one free serverless deployment.