AI API on Arc: deposit USDC on Circle's chain, then pay every model call with a signature
Pay for 89 AI models from USDC on Arc, Circle's network where USDC is the gas: deposit once into Circle Gateway, sign every call off-chain. No second token, no API key. BlockRun Nano.
Arc, in the buyer's terms.
Arc is Circle's own Layer 1, built around USDC as the native asset: it is the gas token, the unit of account and the thing you already hold. That removes the one friction every other chain has for an agent that wants to pay for AI — the need to keep a second token for gas. On Arc a wallet holding only USDC can deposit into Circle Gateway and be calling models a few seconds later.
BlockRun Nano accepts Arc as a Circle Gateway deposit chain. The flow is the one every nano buyer uses: one deposit transaction into Gateway on Arc, then an EIP-712 signature per call, verified by Circle's facilitator before the model runs and settled in batches afterwards. Arc appears in the 402's accepted networks the moment Circle's facilitator lists it, so the SDK never needs a config change to follow the chain.
This page is about paying from Arc through Circle Gateway. BlockRun's native-x402 gateway on Arc — each call settled as its own Arc transaction, without a Gateway deposit — is a separate host, arc.blockrun.ai. Same catalog, same API, different rail; pick the one that matches how your agent holds funds.
What you actually run.
npm install @blockrun/nano-clientimport { NanoClient } from "@blockrun/nano-client";
const client = new NanoClient({ chain: "arc", privateKey: process.env.PRIVATE_KEY });
await client.deposit("5"); // one on-chain tx into Circle Gateway
const r = await client.chat({ model: "openai/gpt-5.5", messages: [{ role: "user", content: "hi" }] });
console.log(r.payment.formattedAmount); // the USD this call cost, signed off-chaincurl -s https://nano.blockrun.ai/.well-known/x402 | jq '.endpoints[0].networks'Arc for pay-per-call AI,
question by question.
- Can I pay for AI API calls with USDC on Arc?
- Yes. Deposit USDC from an Arc wallet into Circle Gateway with client.deposit(), then every call to BlockRun Nano is an off-chain signature against that balance. The 402 lists Arc among the accepted networks whenever Circle's facilitator supports it.
- Do I need a gas token to use the AI API on Arc?
- No. USDC is Arc's gas token, so the deposit transaction is paid in USDC and every call after it is a signature with no gas at all. Arc is the only chain in the list where a wallet holding nothing but USDC can complete the whole flow.
- What is the difference between nano.blockrun.ai and arc.blockrun.ai for Arc?
- nano pays from Arc through Circle Gateway: one deposit, then batched off-chain signatures. arc.blockrun.ai settles each call natively through x402 as its own Arc transaction, with no deposit step. Same models, same prices, same API; choose by whether your agent prefers a prepaid balance or per-call on-chain settlement.
- How does paying on Arc compare with Base, Polygon, or an OpenAI API key?
- Base is blockrun.ai's native x402 rail and is not offered on nano. Polygon works the same as Arc here but needs POL for the deposit gas. An OpenAI key needs a human, a card and a monthly bill; on Arc the wallet is the credential and each call is priced before it runs.
- Which AI models can I call from Arc, and what do they cost?
- The whole BlockRun catalog — 89 models across chat, image, video, music and speech, plus search, markets and RPC — at provider cost plus a 5% margin and a flat $0.002 per call, the same on every chain. The price of a specific call is in the 402 before it runs.
- Is Arc live on BlockRun Nano today?
- Arc is in nano's accepted-chains list and is offered in the 402 whenever Circle's Gateway facilitator reports it as supported. Check the live networks array at /.well-known/x402 — that is the same source the 402 uses, so it is never ahead of what will actually verify.
- Can I move a Circle Gateway balance from Arc to another chain?
- Yes. client.withdraw() with a chain option moves USDC from your Arc Gateway balance to any other supported chain over Circle's CCTP in roughly a quarter of an hour; without the option it returns to your Arc wallet immediately.
- Is there a free way to try the AI API from Arc before depositing?
- Yes — 4 models are free and need no wallet, no deposit and no signature on any chain. Prototype against one, then deposit on Arc when you move to a paid model.