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Public story · 2026-09-17 · high
The update also caps how long headless sessions wait on MCP servers to connect and cuts a redundant model call per background task.
Why now: The changelog entry is dated September 17 and is one of the largest in its recent history.
Claude Code 2.1.274 stops sessions from retrying a corrupted "unexpected tool_use_id" error forever, per Claude Code's changelog. Headless and scheduled sessions had two ways to hang before this release. One was an infinite retry loop on that error; the other was an unbounded wait for MCP servers to connect at startup.
The new CLAUDE_CODE_MCP_STARTUP_WAIT_MS variable bounds how long the first non-interactive turn blocks while connecting to MCP servers. Set it to 0 and the session doesn't wait at all.
Headless and SDK sessions also stop making a separate model call for every finished background task.
The release also adds an effort attribute on the claude_code.llm_request OpenTelemetry span. A new claude_code.managed_settings_resolved OTel event fires when OTEL_LOG_MANAGED_SETTINGS=1 is set. An index.jsonl file now links OTEL_LOG_RAW_API_BODIES output back to the requests that produced it.
/code-review also switches to leaner inline prompts instead of spawning many subagents on untuned models. Bedrock, Vertex, and Foundry installs now default to the v2 MCP client with 2026-07-28 negotiation.
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The default is 200 search calls and 200 subagent spawns per session, adjustable through an environment variable when you hit it.
The August 20 update also lets plugin marketplaces mint short-lived headers instead of storing static tokens in config.
v2.1.211 stops Bedrock, Vertex, Mantle, and Foundry from rebilling cached system context as full-price input tokens.
A hook could exit code 2, report failure, and still let the tool run if its JSON failed schema validation, per Claude Code's changelog.
A repository's settings file could redirect where Claude Code stores config and temp files, before a single prompt ran.
A deny rule with parentheses in the path was silently ignored, leaving files editable that should have been locked down.
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