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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 v2.1.221 Home All releases ←olderv2.1.220 v2.1.222newer→

Claude Code v2.1.221 3 Aug 2026

Cached MCP initialize responses checked against supported protocol versions

You'll notice

Useful3 Signal0

MCP

Cached MCP handshakes with an unsupported protocol version are now thrown away and redone.

What

A stored initialize response for a claudeai-proxy server is now discarded when its protocol version is unsupported, not only when it fails schema validation.

Details

Applies to cachedInitResponse on the claudeai-proxy path.
Previously only an InitializeResult validation failure caused a discard; now an out-of-range protocolVersion does too.
Either failure logs and falls back to a real initialize round trip.

Evidence

falling back to real initialize

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 →