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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 v2.1.205

--append-subagent-system-prompt flag

What

Appends a custom system prompt to every Task-tool subagent launched by Claude Code, propagated recursively to nested subagents.

Usage
claude --print --append-subagent-system-prompt "Always respond in JSON" ...
Details
  • Only works with --print (non-interactive mode)
  • Sets CLAUDE_CODE_ENABLE_APPEND_SUBAGENT_PROMPT=1 automatically
  • Propagates the appended prompt through nested subagent chains
  • Useful for enforcing output format, language, or tool constraints across all agents in a pipeline
Evidence

CLI flag description (search for "Append a system prompt to every Task-tool subagent") — UCp() at line ~763864

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 v2.1.205 →