x402
Also: HTTP 402 · Payment Required
A payment protocol that uses the long-unused HTTP status code 402 to let a machine client pay for a single request, without an account or a subscription.
HTTP has carried a reserved status code for payment since the beginning of the specification, and it went unused because the human web settled on subscriptions and advertising. x402 gives it a job. A server answers a request with 402 and a machine-readable price; the client pays and repeats the request; the resource is returned.
Why it exists now and not in 2005
The pattern only works when the settlement fee is smaller than the thing being bought, and when the buyer is a program rather than a person. An autonomous client cannot type card details and should not hold a subscription to every service it might need once. Cheap settlement plus non-human buyers is what changed.
What a working deployment needs beyond the protocol
- A price quoted in the response, machine-readable, before the client commits.
- A spending limit enforced outside the client rather than inside its prompt.
- A record tying the payment to the decision that caused it.
- A path from that record into ordinary accounting.
None of these are protocol features. They are the wrapper an organisation needs before it will allow the protocol at all, which is why the interesting announcements in this area are about plumbing rather than payments.