Claude Code release notes: 2.1.274 controls MCP startup wait

Claude Code 2.1.274 lets you limit how long the first non-interactive turn waits for MCP servers that are still connecting. It also fixes tool calls timing out after about five minutes despite a longer configured timeout.

MCP (Model Context Protocol) connects Claude to external tools and data sources. These changes cover both the start of an automated run and the calls that follow.

Source: Claude Code 2.1.274 release notes.

Claude Code adds a separate MCP startup wait

The CLAUDE_CODE_MCP_STARTUP_WAIT_MS environment variable caps, in milliseconds, how long the first non-interactive turn waits for connecting MCP servers. Set it to 0 to skip the wait. This controls startup waiting, not how long a tool call can run.

Human step: Use Claude Code 2.1.274 or later and set the variable in the environment that launches your automated run. Choose 0 only if the run can begin without waiting for those connections.

In --input-format stream-json sessions, the first turn also stops waiting up to two seconds for still-connecting servers whose tools are deferred by tool search. Those tools arrive on a later turn.

Source: Anthropic's MCP startup and stream-json changes.

Long MCP calls respect the configured timeout

For Streamable HTTP, an HTTP-based MCP transport, 2.1.274 fixes calls timing out after about five minutes even when the server's timeout was longer. The documented change makes that longer setting work; it does not give every call unlimited time.

Version 2.1.273 also added a notification when an MCP server disconnects during a session and automatic reconnection gives up. It points to /mcp. In 2.1.274, errors also distinguish missing permissions from an expired sign-in for 403 insufficient_scope, directing you to re-authenticate through /mcp.

Sources: Claude Code 2.1.273 release notes. Claude Code 2.1.274 release notes.

Version 2.1.274 was published on September 17 and was the latest version on npm when checked that day.

Source: Claude Code in the npm registry.