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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

Connected client record exposes protocol details and goes through an adoption hook

Under the hood
Useful2 Signal0
MCP

Connected MCP servers now track their negotiated protocol, and a failed wiring step no longer breaks the connection.

What

The object returned for a connected MCP server carries protocol metadata and is handed to a registered wiring callback.

Details
  • The record now includes negotiatedProtocolVersion and protocolEra alongside capabilities and instructions.
  • After building it, the connect path calls a registered wiring callback.
  • If that callback throws, the connection still succeeds and a warning is logged saying the placeholder is retained and adoption will retry.
Evidence

connected-client wiring failed (placeholder retained, adoption will retry)

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 →