Claude Code remembers when a stdio MCP server (a tool server that runs as a local program on your machine) only spoke the older handshake on an earlier connection. Now, if that server returns an error to the older handshake, Claude Code throws away what it remembered and restarts the server once using the newer discovery handshake. Before, only a different failure case tried the newer handshake again on a fresh connection.
The log messages for this were reworded, and the timeout handling when connecting to stdio servers changed.
The server-controlled setting for protocol negotiation on stdio servers now defaults to on when the server sends nothing. It has read on for this site's account and for the anonymous baseline since 2026-09-29.
Stdio MCP servers now try the newer protocol by default, and a server that was wrongly remembered as old-style gets a second chance instead of staying stuck on the older handshake.
tengu_mcp_protocol_negotiation_stdio On for this account, and not off by defaultThe flag server returned on for the one account this site reads, and nothing in this release compiles it off by default. The compiled default is shown below, and says which it is when we cannot read one: a fifth of gates compile in a string or a number rather than on or off, and most published releases have no gate table behind them at all. No client can see what the server returns for your account.
This account: on · anonymous baseline: on · compiled default in v2.1.292: on
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 v2.1.292. It isn't a statement about your account. What a flag value here can and cannot tell you
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.
A reading is one sample. Claude Code evaluates its flags remotely, so no client sees the targeting rule behind a value and this says nothing about your account.