You'll noticeTier: how much it should matter to you
2Useful: my rating, 1 to 5
3Signal: worth watching, 1 to 5
MCPArea: what it touches
New FeaturesKind: in v2.1.251,
New FeaturesSection of the release
What
On hosted sessions, where CLAUDE_CODE_REMOTE is set, an MCP server added at runtime whose name matches a reserved set is refused unless it is an http server on a loopback IP address such as http://127.0.0.1:PORT/mcp. The refusal tells you to point it at the in-container listener or rename the server.
Details
Only reached for dynamically loaded server configs on hosted or remote sessions; local sessions are unaffected.
The address must be a literal loopback IP, not a hostname.
Which names are reserved is decided by an internal list that this build does not spell out.
Evidence
is reserved except as an http server on a loopback IP literal (e.g. http://127.0.0.1:PORT/mcp) and was not loaded, on a hosted session is reserved except as an http server on a loopback IP literal (e.g. http://127.0.0.1:PORT/mcp) and was not loaded
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Added sinceA small documentation edit on Configure cloud environments touched a line naming CLAUDE_CODE_REMOTE after this was published.* **No cloud-only scoping**: hooks run in both local and cloud sessions. To skip local execution, exit early unless the `CLAUDE_CODE_REMOTE` environment variable is `true`, the way the [dependency install script](#install-dependencies-with…cloud-environmentssee the edit
How sure we are
Two sources agreeTwo things we can check say the same as this entry.
Anthropic's documentation agreesA small documentation edit on Configure cloud environments touched a line naming CLAUDE_CODE_REMOTE after this was published.
Anthropic's release notes agreeFixed /mcp reconnect on Remote Control showing a generic withheld-detail error instead of the real remedy when a server was disabled in…
