CLAUDE_CODE_SUBAGENT_MODELU

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_CODE_SUBAGENT_MODELU is a Claude Code environment variable: The trailing-U variant flagged as a likely typo in v2.1.84 has been removed. CLAUDE_CODE_SUBAGENT_MODEL (without the U) remains. Clean housekeeping. Its release history is not tracked here. 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_SUBAGENT_MODELU=<value>
claude

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

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

Release notes that mention it

• Claude Code v2.1.85 — 6 New Environment Variables: MCP Server Config and a 7 MB Diet
• Claude Code v2.1.84 — 6 New Environment Variables: Idle Management and Stream Resilience
• 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_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
• 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.