Accounts are one billing model. Protocol-native payment is another.
Traditional API billing usually starts with account creation and credentials. x402 can expose the payment requirement directly at the resource boundary, letting software discover terms and authorize within its own policy.
Current SML examples use Base/USDC and fresh x402-v2 challenges. Retired GitHub and multi-rail material is not current authority.
Current buyer evidence · GitLab source
Side by side
| Account billing (cards) | x402 payments (USDC) | |
|---|---|---|
| Setup | Sign up, add a card, get an API key | None. Call the endpoint. |
| Smallest practical charge | Limited by fixed card fees | Fractions of a cent |
| Who can pay | People with accounts | Any agent with a wallet |
| Price discovery | Pricing page | Live 402 challenge per request |
| Billing | Monthly invoice | Settled per call |
Which to choose?
Account billing suits human customers on subscriptions, with refunds and invoices handled by the payment provider. x402 suits AI agents and scripts that need to buy one result at a time without a human signing up. Many APIs offer both: a subscription for teams and pay-per-call for machines.
Read x402 vs MPP and the pay-per-call API guide for more.