Definition
MPP — the Machine Payments Protocol — is an open standard developed by Tempo and Stripe that lets AI agents pay for paid APIs autonomously. Instead of signing up, getting an API key, and managing billing, an agent calls a service URL, gets a 402 Payment Required response with a price, pays inline (with stablecoins, cards, or Bitcoin Lightning), and gets the response — all in one request. This makes pay-per-call APIs viable for the first time: no minimums, no subscriptions, no API keys. As of 2025, ~90 services support MPP, including OpenAI, Anthropic, Hugging Face, Cloudflare, and many specialized data providers. Browse the directory at our /services page or read the protocol spec at mpp.dev.