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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.248

MCP tools routed through the REPL instead of the tool list, switched off

Not switched on
Useful2 Signal4
MCP

MCP tools could be called from inside the REPL rather than listed as top-level tools.

The selecting predicate returns false outright, so the alternative wording is unreachable.

Feature flag
tengu_slate_harbor Not enough to say

Nothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.

This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.248: on

Read once, for one account on one subscription tier, against v2.1.248. It isn't a statement about your account. What a flag value here can and cannot tell you

What

Groundwork is present for a mode in which tools from connected MCP servers (external tool servers Claude Code connects to) are called from inside the REPL environment rather than advertised as top-level tools. The predicate that selects this mode is a function whose whole body returns false, so the filter never fires and the wait-for-servers tool always emits the existing wording, "The server's tools should now be available." and "its tools will be added to your tool list". The alternative phrasing describing REPL-callable tools is compiled in but unreachable.

Details
  • MCP authentication stub tools are now tagged isAuthStub: !0 in their server info, a field absent from 2.1.247.
  • Two new helpers read that tag: one narrows a tool list to non-MCP tools plus auth stubs, the other decides whether MCP tools stay deferrable and whether callers pass keepMcp.
  • The REPL surface itself is gated on tengu_slate_harbor, which falls back to false, and applies only to the cli and remote entrypoints.
  • The wait tool still returns ready=true on the existing path, so no behaviour visible to users changes in this build.
Evidence

rather than advertising them as top-level tools). Returns ready=true when, callable inside the REPL environment (this surface routes MCP tools through the REPL rather than advertising them as top-level tools), The server's tools should now be available., tengu_slate_harbor, isAuthStub, keepMcp

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.248 →