CLAUDE_CODE_ENABLE_APPEND_SUBAGENT_PROMPT

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_CODE_ENABLE_APPEND_SUBAGENT_PROMPT is a Claude Code environment variable: Authorizes SDK callers to append a custom string to a subagent's system prompt via options.appendSubagentSystemPrompt. Without this flag, the option is ignored. Capability gate. Added between v2.1.108 and v2.1.114 and still present in v2.1.294. It is not in the official reference.

How to set it

For one session, export it in the shell that starts Claude Code:

export CLAUDE_CODE_ENABLE_APPEND_SUBAGENT_PROMPT=<value>
claude

To apply it to every session, add it to the env object of a settings file:

// ~/.claude/settings.json
{
  "env": {
    "CLAUDE_CODE_ENABLE_APPEND_SUBAGENT_PROMPT": "<value>"
  }
}

Release notes that mention it

• Claude Code v2.1.114 — Native Binary Launcher, /fewer-permission-prompts, and 20 New Environment Variables

Related variables

• CLAUDE_CODE_SUBAGENT_PROMPT_CACHE_TTL
• CLAUDE_CODE_MEMORY_SUBAGENT_APPEND
• CLAUDE_CODE_SUBAGENT_PROMPT_SNAPSHOT
• CLAUDE_CODE_FORK_SUBAGENT: Changelog-confirmed[1]: set to 1 to run subagents as forked processes (v2.1.117 on external builds, v2.1.121 extended to non-interactive SDK/-p sessions).
• CLAUDE_CODE_FORWARD_SUBAGENT_TEXT: Includes subagent text and thinking in stream-json output, paired with a new --forward-subagent-text flag.
• CLAUDE_CODE_MAX_SUBAGENT_SPAWN_DEPTH: Nesting-depth cap on delegation, default 1 — subagents no longer spawn their own subagents, and the team roster stays flat.
• CLAUDE_CODE_SUBAGENT_MODEL: Force a specific model for sub-agent operations.
• CLAUDE_CODE_SUBAGENT_MODEL_FORCE

Frequently asked questions

All variables, searchable: Claude Code environment variables.