Introducing zkAPI: private usage credits for any API

I've been suggesting that crypto is a better way for agents to handle payment for services for a bit. Here is a broader example of generally using crypto to pay for service usage without having to divulge your identity with it.

zkAPI separates payment from identity. You deposit credits (ETH, USDC, etc.) into a vault contract on Ethereum, one ordinary transaction. From then on, your balance exists as a private note: digital cash that only you can spend and that nobody can trace back to the deposit.

To authorize spending, software on your machine produces a small zero-knowledge proof that says, in effect, that a funded note covers this spend and nobody has spent it before. One proof can cover a single request or a whole session. The server can check that the statement is true without learning which note, which deposit, or which person. At the payment layer, requests do not link to you, and they do not link to each other.

I'm glad that folks are thinking about this. The speed of the web shouldn't be limited by the pace of bank settlements and we shouldn't have to forego our privacy in exchange for simply using an API.