How to Track AI API Costs Per Customer With One API Call

Track your AI costs per customer in one API call If you're building on top of AI APIs, you're probably calling OpenAI, Anthropic, Cohere, and a few others depending on the task. Each one bills differently. Costs shift when model prices change. And at some point, someone asks: "Are we making money on this customer?" Without instrumentation, that question takes a day to answer. With it, it takes a query. The problem You ship a feature. It works. Customers use it. Then pricing changes, or a customer's usage spikes, or you realize token costs for one feature are eating your margin on that plan tier. The issue isn't that you don't have cost data — your AI provider invoices you every month. The issue is that data isn't broken down by your customers or your features. You see what you spent. You don't see what each customer cost you. To know your margin per customer, you need to capture cost at the moment the AI call happens — with context attached. One event call After each AI API response, s