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Sweep 22 Oct 2026 · 04:32Z Build v2.1.308 527 read Stable v2.1.308 Latest v2.1.308 Next v2.1.308 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.221 ·

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

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

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JSON All of v2.1.221
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3Signal: worth watching, 1 to 5
MCPArea: what it touches
In DevelopmentKind: in v2.1.221,
In DevelopmentSection of the release

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 →

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