How AI agents pay for APIs: a wallet, not a card
Cards assume a human at signup. An agent holding USDC is a complete customer: it reads the 402 quote, signs the exact amount, and buys — with spending shaped by ceilings, prepaid balances, and revocable keys.
Why cards fail software
Card checkout assumes a human: an account, a billing form, a fraud model trained on people. An autonomous agent stalls at every one of those gates. What software needs is an identity it can hold and a payment it can sign — which is exactly what a wallet is.
Here a wallet holding USDC is the whole customer. No signup, no card on file, no API key exchange. Payment and authentication are the same act.
What a buy looks like
Two HTTP requests. The first, with no payment header, answers HTTP 402 — the machine-readable quote, one entry per network with the exact USDC amount. The agent signs that amount as an EIP-3009 transfer authorization and resends with X-PAYMENT. The answer carries the work and the settlement.
Quoting is free and repeatable, so an agent can price a job across networks before spending anything.
Staying inside a budget
The price is known before the work runs: compute quotes the hours you ask for, inference charges input by byte and output at the ceiling you set. An agent can also prepay a balance and mint revocable bearer keys on it — a key draws from the balance and can never overdraw it, so a runaway agent exhausts its allowance and stops.
For wallet-holding workflows, the MCP server keeps money propose-only: the agent stages a transfer, the human owner approves it.
FAQ
Does an agent need a bank account or card?
No. A wallet holding USDC is a complete customer identity — it quotes, signs, and buys over plain HTTP.
How does the agent know the price before paying?
The 402 response is the quote: it carries the exact amount for that exact request, per network, and producing it charges nothing.
How do I keep an agent from overspending?
Give it a bearer key minted on a prepaid balance — the key can never overdraw the balance. Ceilings price the work before it runs.
Which networks can it pay on?
Each 402 lists every accepted network with its own exact amount; the catalogs at /api/compute/catalog and /api/inference/catalog are the live read.