1.4.0a3

Third alpha of the 1.4.0 line. This release focuses on the new langchain.mcp namespace for adapting MCP servers into LangChain tools.

langchain.mcp highlights

• MCPAdapter adapts any target fastmcp.Client accepts — a URL, a local script, an in-process server, an MCPConfig naming several servers, or a pre-built client — as well as a FastMCP ClientGroup for a fleet of servers behind one client.
• MCPAdapter.list_tools(*, cache_mode="use") discovers and adapts tools, with optional client-side response caching (SEP-2549): use serves a cached list within the server's TTL hint, refresh repopulates it, bypass skips it.
• as_langchain_tool(tool, client, *, elicitation=None) converts a single MCP tool for callers managing their own client.
• Tool metadata is grouped under an mcp namespace on each tool: the tool's annotations (snake_case) and _meta under metadata["mcp"]["tool"], and the serving server's identity under metadata["mcp"]["server"].
• elicitation="interrupt" surfaces a server's mid-call questions as LangGraph interrupts, so a human answers and the run resumes.

from langchain.agents import create_agent
from langchain.mcp import MCPAdapter

async with MCPAdapter("https://example.com/mcp") as adapter:
    agent = create_agent("anthropic:claude-sonnet-5", await adapter.list_tools())

Requires the mcp extra: pip install "langchain[mcp]" (and fastmcp>=4.0.0).

Install

pip install --pre "langchain==1.4.0a3"

This is a pre-release; install with --pre.

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Release notes curated with the assistance of an AI agent.