LangChain Updates Support for MCP Stateless Protocol and Elicitation

LangChain has significantly revamped its Model Context Protocol (MCP) support to reflect the latest stateless specification. With this update, MCP-related code has moved from the separate installation package langchain-mcp-adapters to the main package langchain.mcp. Built on FastMCP, it is compatible with both legacy and new specification versions.

Previously, MCP was a session-based protocol that caused 'sticky routing' issues, binding clients and servers to specific instances. The new specification introduces a stateless core, eliminating these constraints and dependencies on session stores. This resolves the issue of live sessions being dropped during server redeployments, thereby improving scalability and reliability.

Key newly supported features include:

• Elicitation via Interrupts: When a server requests user confirmation or additional parameter input during a call, it is handled in a retryable manner via LangGraph's interrupt mechanism without maintaining the connection.
• Client-side Caching: Servers can specify the validity period of the tool list, allowing clients to cache it instead of fetching the tool catalog on every execution.