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Sweep 22 Oct 2026 · 04:32Z Build v2.1.308 527 read Stable v2.1.308 Latest v2.1.308 Next v2.1.308 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.274 ·

Startup failures are now reported as structured JSON in stream-json/SDK mode

CLI startup failures can now be reported as structured JSON results for SDK and programmatic callers, not just printed to stderr

Group of 5 Use it now Improvements
JSON All of v2.1.274
Use it nowTier: how much it should matter to you
2Useful: my rating, 1 to 5
2Signal: worth watching, 1 to 5
SDKArea: what it touches
ImprovementsKind: in v2.1.274,
What probably matters to youSection of the release

What

  • When Claude Code fails to start (for example: the CLI is too old for the workspace/server, no usable shell tool is found on Windows, proxy configuration is invalid, or another process already holds the session) and is running with --output-format stream-json, it can now emit a structured result message on stdout carrying a machine-readable reason, in addition to (or instead of) the usual stderr text.
  • This reason is carried in a new startup_failure_reason field, with values seen including cli_version_too_old, shell_tool_missing, proxy_invalid, and session_held_by_background.
  • This behavior requires both --output-format stream-json and the environment variable CLAUDE_CODE_STARTUP_FAILURE_RESULTS to be set; the emitting function checks for the env var before doing anything.

Why This lets SDK and other programmatic callers detect exactly why a headless Claude Code process failed to start by parsing structured output, instead of having to scrape human-readable stderr text.

See this entry in the whole of v2.1.274 →

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