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Sweep 22 Oct 2026 · 21:04Z Build v2.1.309 528 read Stable v2.1.308 Latest v2.1.308 Next v2.1.309 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.221 ·

Custom MCP notification handlers skipped on modern-era connections

MCP servers using a newer protocol era no longer get custom notification handlers, and you see a warning.

Nothing to try yet In Development
JSON All of v2.1.221
Nothing to try yetTier: how much it should matter to you
2Useful: my rating, 1 to 5
2Signal: worth watching, 1 to 5
MCPArea: what it touches
In DevelopmentKind: in v2.1.221,
In DevelopmentSection of the release

Protocol-era-aware notification handling only applies when MCP era negotiation flags are on.

What

Registering a handler for an unsolicited custom notification is refused when the connection negotiated a modern protocol era, because there is no delivery path for it.

Details
  • Emits a warning naming the server, the method and the negotiated revision.
  • In 2.1.220 the handler was always registered; getProtocolEra does not appear in that build.
  • Only reachable when era negotiation is on, see the tengu_mcp_protocol_negotiation_* flags.
Evidence

which has no delivery path for unsolicited custom notifications

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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