ClaudeCodeChanges

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Claude docs changes for September 6th, 2026 [diff]

Executive Summary

  • New --append-subagent-system-prompt-file CLI flag lets you load subagent system prompt additions from a file instead of passing them inline, useful for long text.
  • Version 2.1.263 shipped with general bug fixes and reliability improvements.

Claude Code changes

Changed documents

cli-reference [Source]

  • Added a new --append-subagent-system-prompt-file flag that loads text from a file and appends it to subagent system prompts, as an alternative to --append-subagent-system-prompt for text too long to pass on the command line; the two flags can't be combined. Requires Claude Code v2.1.261 or later. [line 58] [Source]

env-vars [Source]

  • CLAUDE_CODE_ENABLE_APPEND_SUBAGENT_PROMPT documentation updated to note it is also set automatically by the new --append-subagent-system-prompt-file flag. [line 245] [Source]

sub-agents [Source]

  • Documented that when subagent system prompt text is too long for the command line, it can be saved to a file and passed via --append-subagent-system-prompt-file (requires Claude Code v2.1.261 or later). [line 223] [Source]