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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.246

Headless startup logs which turn loop it is running

Under the hood
Useful2 Signal3
Headless Mode

Headless runs log which turn loop they're using, making non-interactive problems easier to diagnose.

What

On starting a print/headless run, Claude Code now writes a debug line naming which of its two turn loops is active, which makes headless behaviour easier to triage.

Details
  • Selected by the environment variable CLAUDE_CODE_PRINT_ENGINE_LOOP; the accessor returns its value when set and false otherwise, so the legacy per-turn path is the default.
Evidence

[print] turns run on the engine session (createHeadlessSession)

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.246 →