Tag every API call with a customer ID and feature name, then compute cost per call from token counts against current model pricing. That gives you per-customer cost attribution instead of just an aggregate bill. Budget caps per customer bound the risk — a runaway loop hits the cap instead of your margin. We built this as MarginDash (https://margindash.com) — the cost calculation piece is also available as a free open-source SDK if you just want that part.