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Utter settles genuine sub-cent payments per call. That is only possible on a chain where the gas does not cost more than the call. Arc is Circle’s stablecoin L1, and on Arc the same USDC is both the gas token and the settlement asset, so a fraction-of-a-cent payment clears without a volatile gas fee swamping it. Utter runs on Arc Testnet only.

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Why Arc

On a general-purpose chain, gas is paid in a separate, volatile token. A sub-cent API call would routinely cost more in gas than the call itself is worth, which kills per-call micropayments before they start. Arc removes that problem: gas is USDC. The fee and the payment are denominated in the same stable unit, so the economics of a per-call payment stay sane down to sub-cent amounts. That is the whole reason the escrow money path can charge what it charges.
Utter uses Arc Testnet only. Chain id 5042002, network string eip155:5042002.

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The two-lens USDC

On Arc, one USDC contract wears two hats. The address is the same for both: 0x3600000000000000000000000000000000000000.
The two lenses have different decimals: 6 for the ERC-20, 18 for the native gas token. Always read decimals() at runtime, never hardcode 6 or 18, and never mix a gas-lens amount with an ERC-20-lens amount. Mixing them is an 18-versus-6 decimals bug that silently mis-sizes a payment by a factor of 10^12.
All amount math in the money path is bigint base-unit math that reads decimals(), so a payment computed against the ERC-20 lens is never accidentally interpreted as a gas-lens amount.

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Endpoints

Every settlement produces an on-chain transaction you can open on the explorer. The buyer SDK prints the settlement tx and an explorer link per paid call, so you can watch the debit and the 70/30 split land on-chain.
The pinned contract addresses on Arc Testnet, including PaymentEscrow, the ResourceRegistry, and the ERC-8004 registries, are in addresses. Do not hardcode addresses from this page; read them from the reference, which is the pinned source.

The escrow response gate

The money path Arc’s economics make possible.

Metering and classification

The bigint base-unit math that reads decimals().

Addresses

The pinned contract addresses on Arc Testnet.

Environment

The RPC and chain settings.