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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.

All of v2.1.176 Home All releases olderv2.1.175 v2.1.177newer
Claude Code v2.1.176

MCP First-Party Auth Error Handling

When a first-party MCP server (one using your claude.ai login) rejects the connection, Claude now emits a structured error with code FIRST_PARTY_AUTH_REJECTED and a more actionable message:

  • HTTP 403: explains the token may be missing a required scope, and suggests running /login
  • HTTP 401: tells you the token may have expired, and suggests /login

The new code enables better diagnostics and retry logic — if a 401 occurs after sending an access token, Claude automatically refreshes the token and retries the request once.

Evidence

First-party auth error (search for "FIRST_PARTY_AUTH_REJECTED" and "missing a scope this server needs")

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

See this entry in the whole of v2.1.176 →