Per-Customer Cost Tracking for LLM SaaS: Know Your Margins Before They Disappear

If you are building a SaaS product on top of LLMs or third-party APIs, your costs are not fixed. What you might not know is which customers are responsible for the expensive ones.

The Problem

Most small teams have a rough idea of their total API costs. Fewer have visibility into per-customer margins. Your API provider dashboard and Stripe do not talk to each other, and neither answers the question you actually need: what did it cost me to serve customer X this billing period, by feature?

Without that number, usage-based pricing is guesswork.

Why Existing Tools Fall Short

OpenMeter and Lago are solid open-source metered billing tools, but they are designed to bill outward to customers and require infrastructure like Kafka and ClickHouse that is hard to justify for a small team.

Stripe tells you revenue per customer.…