Per-request AI cost attribution is the difference between rough budget tracking and defensible chargeback.
Multi-tenant gateways hide the real billing path unless you capture tenant, route, model, and token data at the same time.
Vendor cost APIs are useful, but they usually summarize usage into buckets rather than preserve a request ledger.
The most reliable pattern is request IDs plus trace IDs plus normalized token and pricing metadata.
Good attribution systems optimize for auditability first, then dashboards.
