Ethereum Launches zkAPI for Private Payments to AI

The experimental system uses zero-knowledge proofs to issue short-lived API keys that let services bill usage without revealing which on-chain deposit paid.

Overview

The Ethereum Foundation and the Open Anonymity Project launched zkAPI on Ethereum mainnet, which went live Thursday, October 1, 2026, and the project is explicitly labeled experimental.
Users pre-fund an on-chain vault with ETH or USDC and the client records private notes that prove a balance without naming the deposit.
zkAPI uses Groth16 zero-knowledge proofs, Baby-JubJub commitments, a 32-level Merkle tree, and nullifiers so a server can validate payment proofs and issue a short-lived session key with a spending limit.
The system does not hide prompt content, IP addresses, timing, or other network metadata and it includes operational limits such as note expiry, a default 24-hour withdrawal challenge period, and a trusted-setup concern in its published parameters.
The launch shows a practical path for privacy-preserving metered payments for AI and other services, but wider adoption will depend on more testing, clearer user displays of costs and expiry rules, and fixes to the trusted-setup and usability risks.