USDC

Fully reserved dollar stablecoin issued by Circle, the settlement asset used by many agent payment rails including x402.

Agent access

Circle CCTP: Cross-Chain Transfer Protocol: permissionless cross-chain transfers of USDC, EURC and registered third-party tokens.
x402: Open standard for internet-native payments built on HTTP 402, letting APIs and agents pay per request across crypto and fiat networks.
Circle Gateway (Nanopayments): Unified USDC balance across chains with instant cross-chain minting; Gateway Nanopayments enable gasless sub-cent USDC micropayments via x402.

Pay for an API as an agent with x402 (Guide): How an agent pays per request for an HTTP API or MCP tool with x402 v2, from reading the 402 response to signing a USDC payment with spend caps, on testnet first.
Agent that can buy things (Stack): The pieces for an agent that pays for APIs per call with x402 stablecoins and buys from merchants with controlled virtual cards, with spend limits, proof of user intent and a full audit trail.
Pay with x402 (Skill): Read an x402 v2 402 response, check it against a spending policy, pay with an SDK or CLI, and verify the PAYMENT-RESPONSE receipt.