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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

Connection telemetry gains negotiation and protocol fields

Under the hood
Useful2 Signal0
MCP

MCP debug output now shows which protocol version and path a server connection used.

What

MCP connection events now report which protocol path was taken.

Details
  • tengu_mcp_server_connection_succeeded adds negotiationMode, protocolEra, negotiatedProtocolVersion and probeFellBack.
  • tengu_mcp_server_connection_failed adds negotiationMode and probeFellBack.
  • The negotiated version is passed through an allowlist of known revisions and reported as other if it is not one of them.
  • The debug line for a successful connect now prints protocolEra and negotiatedProtocolVersion alongside the capability summary.
Evidence

negotiatedProtocolVersion

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 →