MPP (Machine Payments Protocol) — agent readiness

Publishing an API's prices in its OpenAPI document, so an agent knows what a paid endpoint costs before it calls one.

Why an agent cares

It is the first agent-payment protocol whose terms sit in a document a crawler can read without attempting a payment: the same /openapi.json we already read, annotated with x-payment-info offers. An agent that reads a broken offer plans against a price that is not real, and an operation priced without a 402 response leaves it no way to pay.

Why we do not score it

The discovery extension is a draft in the specification repository, not a submitted Internet-Draft, and the draft itself makes discovery OPTIONAL because the runtime 402 challenge is always authoritative. Score it once the extension is submitted and stable and more than one organisation serves a discovery document.

Adoption

Early pilots. Named early adopters exist, behind flags or trials. Nothing has been independently measured yet. For this one in particular, protocol L2 / discovery documents L1.

Direction of travel: ▲ rising, as at 2026-08-26.

Stripe and Tempo published the protocol in March 2026, Stripe accepts cards and stablecoins through it, and Cloudflare documents it for agents. Live use is still rare: we have found one working discovery document, serving three payable operations.

Adopter	Depth	Evidence
Stripe (payment provider: cards via shared payment tokens, plus stablecoins)	`production`	docs.stripe.com
Parallel (parallelmpp.dev; discovery document verified by probe)	`production`	docs.parallel.ai
Cloudflare (documented for its Agents platform)	`announced`	developers.cloudflare.com

Specifications

Document	Revision	Kind
Service Discovery for HTTP Payment Authentication	Draft	specification
The "Payment" HTTP Authentication Scheme	Draft	specification
MPP documentation	Living document	guidance

Last re-read against the published documents: 2026-10-05.