Per-user cost attribution for your AI APP (opens in new tab)

You ship your AI feature. It works. A week later your OpenAI bill is $400 and you have no idea which of your users caused which $0.05. This is the single most underrated metric in production LLM apps — cost per end-user — and it's surprisingly easy to instrument if you know what to do. Here are the three approaches I've found work in practice, ranked by setup time. Approach 1: Wrap your provider client (5 minutes) Works for Express, Next.js Route Handlers, Fastify — anything that has a single...