LangChain Just Made MCP First-Class — We Ran It the Same Day, and Three Things Don't Work Yet
In July the MCP specification ripped out sessions. We wrote at the time that the change was infrastructure, not changelog — that a stateless core would let servers sit behind ordinary load balancers and survive redeploys, and that clients would need to catch up.
Today LangChain caught up. MCP support moved out of the separate
langchain-mcp-adapters package and into langchain itself, rebuilt on FastMCP,
with two features the old spec made impossible: elicitation as a LangGraph
interrupt, and a cacheable tool catalog.
We installed it the same afternoon and pointed it at a server we wrote against the new spec. The announcement is accurate. The ecosystem around it is not ready — and one of the gaps quietly converts a human-approval gate into a sentence the model invents.