CLAUDE_CODE_SPARE_KEEPS_BOOT_SESSION_ID

Updated November 3, 2026 by Alex Sorokoletov

CLAUDE_CODE_SPARE_KEEPS_BOOT_SESSION_ID is a Claude Code environment variable: When set, keeps the boot session ID so a spare process does not claim a new session when none was provided. Added in v2.1.318 and still present in v2.1.318. 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_SPARE_KEEPS_BOOT_SESSION_ID=<value>
claude

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

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

Related variables

• CLAUDE_BRIDGE_REATTACH_SESSION: Session identity used during bridge reconnection.
• CLAUDE_CODE_BRIDGE_SESSION_ID
• CLAUDE_CODE_CHILD_SESSION
• CLAUDE_CODE_DISABLE_NESTED_SESSION_ID: Set to a truthy value to stop the session-id getter from returning null and have it return the resolved id instead.
• CLAUDE_CODE_EMIT_SESSION_STATE_EVENTS: Controls whether Claude Code emits session state change events.
• CLAUDE_CODE_EVAL_INTERVIEW_SESSION: When set, marks an eval interview session and suppresses the default auto-publishing of the eval report.
• CLAUDE_CODE_FORCE_SESSION_PERSISTENCE
• CLAUDE_CODE_POST_FOR_SESSION_INGRESS_V2: Use POST-based session ingress v2.

Frequently asked questions

All variables, searchable: Claude Code environment variables.