Usage-based billing for AI apps in 2026: Stripe, Metronome, Orb, Lago and Polar compared

The short answer

An AI app pays for every token, so a flat monthly plan loses money on its heaviest users. On our worked example, a $20 plan whose user sends 4,000 requests a month costs $40 in tokens and loses…

Flat plans leak: above about 1,900 requests a month, a $20 user costs more than they pay

Three models: prepaid credits, metered pay-as-you-go, or flat plus overage

Stripe now points new usage billing at Metronome, which it bought in January 2026

Credits don't enforce themselves: Stripe's basic meters and Polar both let users run past their balance

Polar doesn't block usage if the customer exceeds their balance. You're responsible for implementing the logic you need to prevent usage if they exceed it.