Circle has launched its x402 Facilitator Service, enabling API providers, data services and AI agents to receive USDC payments across Arc, Base and Polygon PoS. The service went live on September 16, 2026, the day Circle’s Arc mainnet became publicly available. x402 uses the HTTP 402 "Payment Required" status to embed USDC transfers into web request-response flows. Circle verifies buyers’ signed EIP-3009 authorizations and settles transactions on-chain, removing the need for sellers to operate relayers, fund gas wallets or conduct sanctions screenings themselves. The service uses the "exact" payment scheme and requires a Circle API key, although a keyless trial is available. Circle says 98.8% of early agent-to-agent x402 payment volume used USDC after it launched its Agent Stack in May 2026. Arc is an EVM-compatible Layer 1 blockchain using USDC as its gas token, with BlackRock, DTCC and Visa among its founding validators. More than 100 partners and applications were operational at launch, while the testnet processed between 500 million and 700 million transactions. Circle minted the full supply of 10 billion ARC tokens but has made no commitment to a public token launch. Extending the service to Base and Polygon PoS broadens access beyond Circle’s own chain, but also concentrates the facilitator, primary blockchain and stablecoin under one corporate umbrella.