What are USDC pay-per-call APIs?

USDC pay-per-call APIs are HTTP APIs that settle each request on-chain in USDC stablecoin instead of charging a monthly subscription or requiring a pre-issued API key.

A pay-per-call API charges for each request rather than per month. Settling those payments on-chain in USDC, typically over the x402 protocol, turns the API into something an autonomous agent can use without human credential management.

Why agents prefer it: no key to rotate, no monthly invoice to reconcile, and the chain handles trust. Why publishers prefer it: revenue scales with use, sub-cent unit pricing is practical on Stellar, and there's no integration work to bill a new customer. A wallet address is all you need.

Related answers

What is x402?
x402 is an HTTP-native micropayment protocol that uses the HTTP 402 "Payment Required" status code to settle paid API calls on-chain in stablecoin in a single round-trip, with no API keys.
How do AI agents pay for APIs and data?
AI agents pay per call in stablecoin over the x402 protocol: the server returns HTTP 402 with payment requirements, the agent's wallet signs an on-chain payment proof, and the server delivers the resource in the same request.
What is an agent marketplace?
An agent marketplace is a venue where autonomous AI agents discover, preview, pay for, and integrate machine-payable assets (datasets, APIs, workflows, and native AI products) without a human in the transaction loop.