2026.08.05x402 Native Payments: HTTP 402 Protocol for AI Agents20 min read x402 UML sequence diagram Twelve numbered steps across four lifelines. Solid arrows are requests, dashed arrows are responses, and self-messages are local work. An alt fragment splits the flow after verification: the invalid branch returns another 402 and stops, the valid branch settles the payment on-chain and returns the resource. x402 payment sequence solid = request · dashed = response · self-message = local work Client Resource Server Facilitator Blockchain alt [invalid] [valid] discover authorize verify settle & respond 1 · GET /weather 2 · 402 Payment Required PAYMENT-REQUIREDprice · tokennetwork · payTo 3 · Sign authorization EIP-3009 · signed locally 4 · Retry + signature PAYMENT-SIGNATURE 5 · POST /verify 6 · VerificationResponse isValid 402 + PAYMENT-REQUIRED client re-signs or aborts 7 · Fulfill resource prepare the paid work 8 · POST /settle 9 · Execute payment transferWithAuthorization 10 · Confirmed 11 · SettlementResponse success · tx hash 12 · 200 OK + data PAYMENT-RESPONSE Client Resource Server Facilitator Blockchain
