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 this container already fetches, 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.

Co-authored by Stripe and Tempo and published on 2026-03-18, with Stripe accepting cards and stablecoins through it and Cloudflare documenting it for agents. A Lumar probe on 2026-08-26 found one live discovery document: Parallel's gateway serves three payable operations, each carrying a conformant x-payment-info offer and a 402 response.

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-payment-discovery-01`	specification
The "Payment" HTTP Authentication Scheme	`draft-ryan-httpauth-payment-01`	specification
MPP documentation	`living`	guidance

Last re-read against the published documents: 2026-08-26.