MPP
Machine Payments Protocol
A turnstile that takes a tap of your card. No account, no membership; pay and walk through.
Reality check
Early use, live on Tempo. Unlike x402, no neutral foundation owns it; it's written and maintained by two companies with a commercial stake.
How it works
Paying for an online service usually means signing up, getting a key and setting up billing, which an autonomous agent can't easily do. MPP uses the web's long-unused "402 Payment Required" code: the server replies "this costs 2 cents, here's how to pay," the client pays, and the server returns the result plus a receipt.
It supports one-off charges, subscriptions and streaming pay-as-you-go "sessions," with stablecoins on Stripe's Tempo blockchain or ordinary cards through Stripe. Picture a research agent paying a fraction of a cent per article from a paywalled archive and settling the total when it finishes.
Who's behind it
Stripe and Tempo launched it on March 18, 2026, the same day Tempo's payments blockchain went live. Its core spec is an IETF Internet-Draft (draft-httpauth-payment-01, September 9, 2026), but an individual one: the IETF lists it as having no formal standing, and no working group has taken it on.
The ecosystem is growing (Circle drafted a USDC payment method), and MPP now accepts x402's simplest payment flow from the same toolkit.