CLAUDE_CODE_FORK_SUBAGENT

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_CODE_FORK_SUBAGENT is a Claude Code environment variable: 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). Forked subagents get true process isolation and independent resource limits instead of in-process coroutines. Added between v2.1.114 and v2.1.117 and still present in v2.1.294. It is listed in the official reference.

How to set it

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

export CLAUDE_CODE_FORK_SUBAGENT=<value>
claude

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

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

Release notes that mention it

• Claude Code v2.1.123 — Background Daemons, Agent Fleets, and CoWork Memory
• Claude Code v2.1.118 — 10 New Environment Variables: Forked Subagents Ship, Subscription Tiering Takes Shape
• Claude Code Version Tracker: Undocumented Env Vars, Feature Gates & Models

Related variables

• CLAUDE_CODE_ENABLE_APPEND_SUBAGENT_PROMPT: Authorizes SDK callers to append a custom string to a subagent's system prompt via options.appendSubagentSystemPrompt.
• 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
• CLAUDE_CODE_SUBAGENT_MODELU: The trailing-U variant flagged as a likely typo in v2.1.84 has been removed.
• CLAUDE_CODE_SUBAGENT_PROMPT_CACHE_TTL
• CLAUDE_SUBAGENT_BG_SHELL_MAX_MS: Time cap for shell commands run by background subagents.

Frequently asked questions

All variables, searchable: Claude Code environment variables.