Ethereum Foundation launches zkAPI to pay for AI APIs without an identity

Victoria Shinder02 October 2026, 07:432 min read

The Ethereum Foundation has introduced zkAPI, a system for paying for metered APIs, AI models in particular, without the payment being tied to an identity. It was built by the Open Anonymity Project with the Foundation and, according to the announcement on 1 October, runs on Ethereum mainnet today.

The problem it sets out to solve is that every AI API call today carries an identity: the key points to an account, the account to a payment method, and every prompt joins a record attached to both. The Foundation argues that prompts are personal, since people ask models about their health, money and doubts, and that the alternatives so far were to pay per request on-chain, which is slow, expensive and traceable, or to trust a middleman.

In zkAPI a user deposits credits, in ETH, USDC or other assets, into a vault contract in one ordinary transaction. The balance then exists as a private note. To spend, software on the user's device produces a zero-knowledge proof that a funded, unspent note covers the cost, and the server verifies it without learning which note or deposit it came from. Deposits sit as commitments in a Merkle tree, and every spend publishes a nullifier, a one-way serial number; spending the same balance twice produces a duplicate nullifier and exposes only that attempt.

In the main mode, the server mints a short-lived API key capped in dollars, which exists only in the device's memory, and prompts go straight from the device to the AI provider. When the key expires, the provider records the total usage in a signed receipt and the server deducts it from the note. The Foundation says the server that handles money never sees content, and the provider that sees content never learns the billing identity behind the key. A simpler proxy mode, where the zkAPI server relays requests, is easier to run but lets the relay see traffic.

Why it matters

Ethereum has long promised privacy for payments; this is a narrow, working application of it to something people use daily. The design's limit is stated in the announcement itself: the provider still sees every prompt, only without a name attached.