Machine Payments Protocol (MPP)

MPP · Stripe MPP · machine-to-machine payments protocol

Definition

MPP (Machine Payments Protocol) is an open protocol from Stripe and Tempo for machine payments for services: the server sets the price with an HTTP 402 response, and the client pays with a method of its choice and receives the resource with a receipt.

What MPP is and why it appeared

Buying a service today often forces an agent to create an account, work through a pricing page, pick a subscription tier and enter payment details — steps that usually need a human. MPP replaces them with a single exchange: the service states the price in its response, the agent pays and gets the result straight away. The protocol covers one-off payments, subscriptions and per-request micropayments for an API, an MCP server or any HTTP endpoint.

How a payment works

Step	What is sent	Where
1. Resource request	An ordinary HTTP request	—
2. Challenge	A 402 response: price, payment methods, expiry	`WWW-Authenticate: Payment` header
3. Credential	The retried request with proof of payment	`Authorization: Payment` header
4. Receipt	The resource and a receipt for the payment	`Payment-Receipt` header

The payment type is set by an intent: charge for a one-off payment, session for streaming payment, subscription for a recurring one. In a session the client makes a single deposit, then signs off-chain vouchers for each request, and the server periodically settles the net amount — which keeps sub-cent payments from being eaten by fees.

Payment methods and governance

As of September 2026, stablecoins on the Tempo network, cards through Stripe and bitcoin through Lightning are in production, and anyone can define their own method. Each method’s specification is maintained by the owner of that payment rail, while the core is published at the IETF as an individual Internet-Draft — no working group has adopted it yet and it is not an RFC. Official SDKs are available for languages including TypeScript, Python, Rust and Go.

	MPP	x402	ACP
What is paid for	Services and resources	Services and resources	A store’s goods
Payment methods	Stablecoins, cards, Lightning	Blockchain networks	Cards via a token
Authors	Stripe and Tempo	Coinbase, now the x402 Foundation	OpenAI and Stripe

What it means for a retailer

MPP does not replace a shopper’s basket: orders from AI agents arrive through checkout protocols.
If you sell a digital service — price and availability data, content, a partner API — MPP lets you charge per request with no contract and no customer account.
On Stripe these payments appear in the Dashboard as ordinary transactions, with tax, fraud protection, refunds and the standard payout schedule.
Agent card payments through Stripe in MPP use the Shared Payment Token, so ACP orders and MPP payments run on the same Stripe infrastructure.

Frequently asked questions

How is MPP different from x402?

Both protocols use the 402 status code, but they are built differently. x402 defines settlement schemes on blockchains and carries its data in its own PAYMENT-REQUIRED and PAYMENT-SIGNATURE headers. MPP is built as an HTTP authentication scheme — WWW-Authenticate, Authorization, Payment-Receipt — and is not tied to blockchains: it also covers cards and Lightning. The MPP SDK can serve x402 clients on the same endpoint.

How is MPP different from ACP?

ACP (OpenAI and Stripe) is a protocol for buying goods from a store inside an AI conversation: catalogue, basket, checkout. MPP is about machines paying for services: an API call, a browser session, per-item access to data. The shared piece is the Shared Payment Token, which Stripe also uses to accept card and buy now, pay later payments over MPP.

Who already accepts payments through MPP?

Stripe's announcement of 18 March 2026 names Browserbase (paying for headless browser sessions), PostalForm (printing and posting letters), Prospect Butcher Co. (ordering sandwiches in New York City) and Parallel Web Systems (paying per API call for web access). A directory of connected services is kept on the protocol site, mpp.dev.

Does an online store need MPP?

For selling goods to shoppers, not yet: that is the job of order protocols such as ACP and UCP. MPP is useful if you sell a digital service per use: an API with prices and availability for partners, data, content generation. According to Stripe, a merchant on Stripe needs only a few lines of code with the PaymentIntents API to accept MPP payments.