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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 v2.1.221 3 Aug 2026

MCP HTTP auth errors matched on both code and errorCode

Under the hood

Useful2 Signal0

MCP

Claude recognizes MCP login failures more reliably, so auth errors are handled instead of retried blindly.

What

The MCP SDK moved to string error codes such as CLIENT_HTTP_AUTHENTICATION carried on a code property, and the app's classifiers were widened to match.

Details

The 401 and 403 classifiers accept either code or errorCode.
The retry predicate special-cases the typed HTTP error's status instead of string-matching "Server returned 403 after trying upscoping".

Evidence

ClientHttpForbidden

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

See this entry in the whole of v2.1.221 →