Your balance lives in Circle Gateway, not on the router. The router can only move money out of it by signing a charge for a request you actually made, and you can withdraw the rest at any time.

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Deposit

Open Overview → Deposit USDC and send USDC to the address shown, on Arc. That address is your own wallet, not Circle’s contract — so it does not matter where the USDC comes from. An exchange withdrawal, a hardware wallet, another account: all fine. The router sweeps what lands there into Gateway by depositing from your wallet, which is what makes the balance spendable on your behalf.
Do not send USDC straight to the GatewayWallet contract.Circle Gateway credits whoever deposited, and honours signatures only from that same address. A transfer into the contract from an exchange or any other wallet creates a balance keyed to that address, which the router can never spend for you. The money is not lost, but it is not usable here either.Send to the address the dashboard shows you and let the sweeper do the deposit.
What lands in the wallet is swept into Gateway automatically, usually within a minute. You can also move it yourself from Deposit USDC → Move from your wallet. The balance shown on Overview is the Gateway figure, and that is the one requests are paid from. A wallet balance that has not been swept yet will not pay for anything.

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How much to start with

5coversalot.At5 covers a lot. At 1/$5 per million tokens, an ordinary chat turn is a fraction of a cent. The figure that actually constrains you is not your monthly spend — it is the hold. Each request holds its full quote until it settles, and the quote is priced at your max_tokens. A balance of $0.50 running requests with max_tokens: 64000 on gpt-6-astra will refuse its own second call, because the first one’s hold has not cleared yet. If you are getting 402 on an account that visibly has money, lower max_tokens before you top up.

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Verify it is really there

The dashboard reads your balance from Circle. If you want to confirm it against the chain itself, the Withdraw dialog reads the contract directly — same number, different source.

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Withdraw

Two balances, and they come back separately:

Gateway balance

USDC you deposited and have not spent. Withdraws to your wallet.

Credit

Refunds from requests that cost less than their quote. Withdrawable.
Credit is withdrawable less any outstanding debt from a turn that settled above its quote. That debt is collected on your next request; until it is, it is held back from withdrawal. See How billing works.

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Gas

You need none. On Arc, USDC is the native gas token, and the router pays the gas on every charge it signs. You will never be asked to hold a second asset to use the API. The one exception is the deposit itself, if you are moving USDC in from an external wallet on a chain where gas is a separate token — that transaction is yours and you pay for it like any other transfer.