feat(anthropic): support for mcp toolset tool

[christian-bromann]

Adds support for Anthropic's MCP (Model Context Protocol) connector feature, which enables Claude to connect to remote MCP servers directly from the Messages API without implementing a separate MCP client.

Motivation

The MCP connector is a new Anthropic feature (beta: mcp-client-2025-11-20) that allows users to access tools from MCP servers through a simple API configuration. This eliminates the need to implement a separate MCP client while still benefiting from the MCP ecosystem of tools.

Usage

import { ChatAnthropic, tools } from "@langchain/anthropic";

const llm = new ChatAnthropic({
  model: "claude-sonnet-4-5-20250929",
});

// Basic usage - enable all tools from an MCP server
const response = await llm.invoke("What tools do you have available?", {
  mcp_servers: [{
    type: "url",
    url: "https://example-server.modelcontextprotocol.io/sse",
    name: "example-mcp",
    authorization_token: "YOUR_TOKEN",
  }],
  tools: [
    tools.mcpToolset_20251120({ serverName: "example-mcp" }),
  ],
});

// Allowlist pattern - enable only specific tools
const response2 = await llm.invoke("Search for events", {
  mcp_servers: [{
    type: "url",
    url: "https://calendar.example.com/sse",
    name: "google-calendar-mcp",
  }],
  tools: [
    tools.mcpToolset_20251120({
      serverName: "google-calendar-mcp",
      defaultConfig: { enabled: false },
      configs: {
        search_events: { enabled: true },
        create_event: { enabled: true },
      },
    }),
  ],
});

[changeset-bot]

🦋 Changeset detected

Latest commit: 7c13d9d

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@langchain/openai	Minor
@langchain/anthropic	Patch
@langchain/classic	Patch
@langchain/community	Patch
@langchain/deepseek	Patch
@langchain/xai	Patch

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[hntrl]

Why not define this inside of the tool definition?

tools.mcpToolset_20251120({
  servers:     {
      type: "url",
      url: "https://example-server.modelcontextprotocol.io/sse",
      name: "example-mcp",
      authorization_token: "YOUR_TOKEN",
    },
}),

[christian-bromann]

Why not define this inside of the tool definition?

Because the tool defines configuration for a single MCP server. If we would extend that to allow configuring all server and their configuration, the tool would have to return an array of tools which seems awkward. Plus, mcp_servers seems like a reasonable property to add since we also have other tool properties on their like container.