This spec documents how to implement the ANT_ONLY_METADATA_USER_ID
environment variable feature that allows internal Anthropic jobs
(Oracle, Oncall, Ambient, etc.) to pass custom metadata through
Claude Code sessions to the API for usage tracking and incident triage.
Key points:
- Read ANT_ONLY_METADATA_USER_ID env var
- Pass value as metadata.user_id in API requests
- Use tree shaking to restrict to internal builds only
- Expected format: {"user": "<username>", "job": "<job_name>"}
