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Sweep 19 Sep 2026 · 02:36Z Build v2.1.278 500 read Stable v2.1.267 Latest v2.1.278 Next v2.1.278 Feeds RSS JSON llms.txt Unofficial
Claude Code v2.1.274 ·

New stdio MCP protocol-negotiation gate added

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A new gate lets stdio MCP connections also try the newer protocol-negotiation handshake

TierNothing to try yethow much it should matter to you
Useful2my rating, 1 to 5
Signal3worth watching, 1 to 5
AreaMCPwhat it touches
KindIn Developmentin v2.1.274,
Nothing to try yet No documentation found

A new gate lets stdio MCP connections also try the newer protocol-negotiation handshake

What

MCP servers connected via stdio (standard input/output, a local process-based connection type) can now use the same automatic protocol-version negotiation that other connection types have, including their own probe timeout setting, instead of always using the older legacy handshake.

Why

This extends newer protocol-negotiation support to stdio-based MCP servers, though it is controlled by a gate that determines whether it's actually turned on for a given account.

Read from
Names in the bundletengu_mcp_protocol_negotiation_stdio
Feature flag
tengu_mcp_protocol_negotiation_stdio Off in both readings

The flag server returned off for the account this site reads and for the anonymous baseline. A reading of off cannot rule out a rollout these two readings sit outside of.

This account: off · anonymous baseline: off · compiled default in v2.1.274: off

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.274. It isn't a statement about your account. What a flag value here can and cannot tell you

How sure we are
One source agreesOne thing we can check says the same as this entry.
The name it cites is new in this buildNew in this build: tengu_mcp_protocol_negotiation_stdio

See this entry in the whole of v2.1.274 →