Protocols
x402
x402 is an open payment protocol that uses HTTP 402 so a client, including an AI agent, can pay a resource server and retry the same request. A facilitator can verify the signed payment and settle it on a blockchain. Version 2 carries the payment requirements in the PAYMENT-REQUIRED header.
Explanation
Coinbase published the launch post on 6 May 2025, which is also the day this index starts its x402 backfill. The version 2 specification separates three layers: shared types such as PaymentRequired and PaymentPayload, scheme logic such as exact or upto, and a transport such as HTTP. On HTTP, an unpaid request gets status 402 and a base64 PaymentRequired object in PAYMENT-REQUIRED. The client signs a payment and retries with PAYMENT-SIGNATURE. After settlement the server returns PAYMENT-RESPONSE.
The default payment flow is authorization: verify, run the resource, then settle. Upfront settlement commits funds before the resource runs, which the spec uses for networks without a pull-payment primitive. An escrow flow settles once before the work and again for the final charge. Those flows, and the exact, upto, and batch-settlement schemes, are not separate protocols. On the chains this index scans, the public evidence is the USDC transfer the payer authorized inside a facilitator transaction. A router that forwards that payment counts once, from the buyer to the final seller. The transfer log does not record the scheme, so stored rows use scheme transfer.
Current index
Data as of Oct 25, 2026, 3:56 AM UTC.
| Period | Volume | Payments | Payers | Sellers |
|---|---|---|---|---|
| 24 hours | $10,898 | 113,369 | 25,547 | 8,644 |
| 7 days | $40,132 | 186,961 | 3,727 | 2,456 |
| 30 days | $45,963 | 215,671 | 3,792 | 2,482 |
Backfill in progress on base, solana, tempo. A checkpoint is still open, so recent totals can still move.
Live data
Related terms
Sources
- Introducing x402 — Coinbase
- x402 Protocol Specification, version 2 — Coinbase x402
- x402 HTTP transport, version 2 — Coinbase x402
- How x402 works — Coinbase Developer Platform
- Agent GDP methodology — Agent GDP