Claude Code v2.1.221 ·
Connection telemetry gains negotiation and protocol fields
MCP debug output now shows which protocol version and path a server connection used.
Under the hoodTier: how much it should matter to you
2Useful: my rating, 1 to 5
0Signal: worth watching, 1 to 5
MCPArea: what it touches
Internal ChangesKind: in v2.1.221,
Internal ChangesSection of the release
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 →
