Source Intelligence
Follow Discord

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

Failed negotiation probes now respawn or reconnect the server pinned to legacy

Not switched on
Useful2 Signal3
MCP

Failed protocol probes would respawn or reconnect the MCP server on legacy, but auto mode is off.

Legacy fallback for failed MCP protocol probes, including stdio respawn, exists but only runs in auto mode, which no gate enables.

What

A probe that fails with EraNegotiationFailed gets the server back on a legacy connection rather than failing the connect outright.

Details
  • stdio servers, which some implementations hard-close before init, are respawned from the saved spawn config and reconnected with { mode: "legacy" }.
  • http and claudeai-proxy servers are rebuilt from a saved transport factory and reconnected.
  • The retry gets whatever is left of the connect budget, floored at 1000ms.
  • The fallback is recorded as probe_failed or closed and reported as probeFellBack.
  • Only reachable when negotiation is in auto mode, which no gate enables in this build.
Evidence

version negotiation probe closed the stdio server (rmcp-class pre-init hard close); respawning pinned legacy

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 →