MCP server now supports list-changed and progress notifications

Group of 3 You'll notice

claude mcp serve now tells clients when its tool list changes and reports progress during long tool calls

What

claude mcp serve now advertises a listChanged tools capability and sends a tools/list_changed notification whenever the visible set of tools changes (for example after a policy-verdict refresh), using a new debounced watcher.
Tool call handling now reads the progress token (_meta/sendNotification) from the incoming request and opens a progress-tracking resource for the duration of the call.
While a long-running tool call executes, the server sends periodic notifications/progress messages ("Running for Ns") on an interval, using that progress token.

Why

MCP clients connected to Claude Code's built-in server can now stay in sync when the available tools change, and can show live progress instead of appearing stuck during slow tool calls.

How sure we are

One source agreesOne thing we can check says the same as this entry.

Anthropic's release notes agreeFixed sustained high CPU usage and repeated tool-list requests when an MCP server sends list_changed notifications in a tight loop

See this entry in the whole of v2.1.271 →

The build it came inv2.1.271

14 Sep 2026 · 420 entries, this one is #79.

Use it now37
You'll notice128
Nothing to try yet21
Under the hood234

Open the release →

Anthropic's notes

Upstream's own release notes for v2.1.271 name something this entry names, so the two are probably about the same change. Probably: the pairing is made on a shared name rather than on the words around it.

Fixed sustained high CPU usage and repeated tool-list requests when an MCP server sends list_changed notifications in a tight loop
Improved claude mcp serve: a running tool call now sends a progress update every 30 seconds, so clients show it is still running and idle timeouts don't abort a long command that prints nothing

Either side of it

v2.1.270Older
v2.1.272Newer

Is this right?