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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 v2.1.232

MCP servers that reply badly to the version probe now fall back to legacy instead of failing

You'll notice
Useful3 Signal2
MCP

MCP servers that reply oddly to the version probe now fall back to legacy instead of failing.

What

When connecting to an MCP server, Claude Code sends a server/discover probe to work out which protocol version to use. It previously handled only a proper response, a send error, a closed connection or a timeout. Three more bad-reply shapes are now recognised and all three are treated as evidence the server is an older one, so the connection falls back to the legacy path rather than failing negotiation outright.

Details
  • New outcomes: id-mismatch (the reply does not echo the request id, seen with HTTP transports), malformed (the reply fails JSON-RPC decoding) and stream-end (the request stream ends with no reply at all).
  • Named errors for these cases are passed to the transport's error handler.
Evidence

server/discover probe reply did not echo the request id (expected

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

See this entry in the whole of v2.1.232 →