CLAUDE_CODE_NANKEEN_KESTREL

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_CODE_NANKEEN_KESTREL is a Claude Code environment variable: Windows-only sandbox gate. The gate function returns false on any non-Windows OS, true if this variable is set, otherwise defers to the server gate tengu_nankeen_kestrel (default off). Added between v2.1.143 and v2.1.212 and still present in v2.1.294. It is not in the official reference.

Status	Present in v2.1.294
Added	Added between v2.1.143 and v2.1.212
Category	Other
Official docs	Not listed

How to set it

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

export CLAUDE_CODE_NANKEEN_KESTREL=<value>
claude

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

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

Release notes that mention it

Related variables

CLAUDE_CODE_GAULT_KESTREL
ANTHROPIC_BETAS: Comma-separated beta feature headers.
ANTHROPIC_CUSTOM_HEADERS: Custom HTTP headers (newline-separated Key: Value).
ANTHROPIC_FEDERATION_RULE_ID
ANTHROPIC_ORGANIZATION_ID
ANTHROPIC_WORKSPACE_ID
BETA_TRACING_ENDPOINT: Custom endpoint for beta tracing.
CLAUDE_AFK_COUNTDOWN_MS

Frequently asked questions

What does CLAUDE_CODE_NANKEEN_KESTREL do?

Windows-only sandbox gate. The gate function returns false on any non-Windows OS, true if this variable is set, otherwise defers to the server gate tengu_nankeen_kestrel (default off).

Which Claude Code version has CLAUDE_CODE_NANKEEN_KESTREL?

Added between v2.1.143 and v2.1.212 and still present in v2.1.294.

How do I set CLAUDE_CODE_NANKEEN_KESTREL?

Export it before starting Claude Code (export CLAUDE_CODE_NANKEEN_KESTREL=value), or add it to the "env" object in ~/.claude/settings.json to apply it to every session.

All variables, searchable: Claude Code environment variables.