x402
Also called x402 protocol, HTTP 402 payments
x402 answers a specific, longstanding annoyance in machine-to-machine
payments: an API wants to charge per call, an AI agent wants to pay for
exactly the calls it makes, and neither wants to set up a merchant
account, an API key with a billing plan, or a human in the loop to approve
each transaction. x402 does it inside plain HTTP: a server that wants
payment answers a request with the (long-dormant) 402 Payment Required
status code plus machine-readable payment instructions; the client retries
the request with a signed stablecoin payment attached; a "facilitator"
verifies and settles it. No account, no session, no card-on-file, just an
HTTP round trip with a payment folded in.
Where it comes from
x402 was created by Coinbase and first released in 2025. On 2026-07-14, Coinbase completed contributing it to a newly launched x402 Foundation under the Linux Foundation, with Adyen, AWS, American Express, Circle, Cloudflare, Google, Mastercard, Stripe, and Visa among more than 40 founding member organizations. It is now a vendor-neutral open standard stewarded by a foundation, not a single company's proprietary rail. Solidus did not design any part of it.
Solidus status
Two different things are easy to conflate here, and it's worth keeping
them separate on purpose. What's shipped: Solidus Agents issues an
AP2-aligned "spend mandate" credential (a BBS+-carried, revocable
statement that "agent X may spend up to $Y on behalf of verified principal
Z") with a generic rail field that can name x402 as the settlement rail
it authorizes. That's an authorization layer, live on
agents.solidus.network's public testnet. What's not shipped: an
actual x402 facilitator, something that accepts the HTTP 402 handshake
and actually settles a payment. That would be pay.solidus.network,
publicly documented internally as "Status: Planned," and as of this
writing the domain doesn't even resolve. Solidus authorizes agent spending
today; it settles no x402 payment.
Proof: the authorization layer is checkable,
agents.solidus.network's mandate endpoints accept a rail field and
issue a credential referencing it (testnet only). There's nothing to
demonstrate on the facilitator side: curl https://pay.solidus.network
fails to resolve at all, which is itself the honest confirmation that this
half doesn't exist yet.
Where it comes from
Someone else specified this. Solidus assembles it.
x402 is an open protocol, created by Coinbase and first released in 2025, that revives the long-dormant HTTP "402 Payment Required" status code: a server can answer a request with 402 plus machine-readable payment instructions, the client (human or, increasingly, an AI agent) attaches a signed stablecoin payment to a retried request, and a "facilitator" verifies and settles it, all inside ordinary HTTP, no account or card-on-file needed. On 2026-07-14, Coinbase completed contributing x402 to a newly launched x402 Foundation under the Linux Foundation, with Adyen, AWS, American Express, Circle, Cloudflare, Google, Mastercard, Stripe, and Visa among more than 40 member organizations: it is now a vendor-neutral open standard, not a Coinbase-only protocol. Solidus did not design any part of it.
How to check this
Planned. Nothing built.
The spend-mandate authorization layer is live: `agents.solidus.network`'s mandate endpoints accept a `rail` field and issue a credential referencing it (testnet only). There is nothing to demonstrate on the facilitator side, `curl https://pay.solidus.network` fails to resolve at all, which is itself the honest proof that this half doesn't exist yet.