x402 on HPP
x402 is an open payment protocol that revives the long-dormant HTTP 402 Payment Required
status code. It lets any HTTP endpoint charge for access with onchain stablecoins — no API keys,
no accounts, no manual invoicing. A client requests a resource, receives a 402 with machine-readable
payment terms, pays by signing a stablecoin authorization, and retries. Settlement happens onchain.
HPP runs production x402 facilitators on both its Mainnet and Sepolia networks, so you can monetize an API — or pay for one — using USDC.e with a few lines of code.
Why x402
- Built for agents and machines. Payment is a single signed message on a standard HTTP response. No human-in-the-loop, no dashboard signup. AI agents can discover a price and pay it autonomously.
- No accounts, no custody. Payment moves from the buyer's wallet to the seller's
payToaddress; HPP's facilitator never custodies funds — it only verifies the signature and submits the settlement transaction (a direct transfer forexact, or a Permit2 transfer forupto). - Stablecoin-native. Prices are quoted in USDC.e. What the buyer signs is what the seller receives.
- Open standard. x402 is maintained by the x402 Foundation,
and HPP uses the same
@x402SDK that works on Base, Polygon, and others — pointed at HPP's networks and facilitator. One small setup step registers USDC.e as HPP's default asset (shown in the quickstarts).
What HPP provides
| Piece | What it is |
|---|---|
| Facilitators | Hosted verify / settle services for HPP Mainnet (facilitator.hpp.io) and HPP Sepolia (facilitator-sepolia.hpp.io). See Facilitator. |
| Networks | HPP Mainnet (eip155:190415) and HPP Sepolia (eip155:181228), recognized natively by the @x402 SDK. See Networks & Token. |
| Token | USDC.e (Bridged USDC) at 0x401eCb1D350407f13ba348573E5630B83638E30D on both chains. |
| Schemes | exact (EIP-3009) and upto (Permit2 with optional gasless settlement). See How it works. |
Where to go next
- How it works — the
402flow, the three roles, and the payment schemes. - Networks & Token — chain IDs, RPC endpoints, and the USDC.e asset.
- Quickstart: Sellers — charge for an HTTP endpoint.
- Quickstart: Buyers — pay for an x402 endpoint from a client or agent.
- Facilitator — endpoints, supported schemes, gasless settlement, and self-hosting.