Vitalik Buterin's zkAPI Payment System Launches on Ethereum Mainnet
The Ethereum Foundation has launched zkAPI, an AI payment system co-designed by Vitalik Buterin, on the Ethereum mainnet. The announcement on October 1 highlighted a key challenge for users: recovering unspent funds when the billing server becomes unresponsive.
zkAPI, a billing system for metered APIs, provides an on-chain withdrawal mechanism that does not require server approval. However, users' ability to recover their balances depends on their spending state and the timeliness of their withdrawal attempt. The system includes pause powers and expiring notes to manage these withdrawals.
The implementation was developed by Open Anonymity in collaboration with the Ethereum Foundation. The underlying design was published by Davide Crapis and Vitalik Buterin on February 11. The system's vault, created on September 30, initially held USDC credits but now operates with native ETH, tracked in whole gwei.
Users have two routes to withdraw funds. The cooperative route, or mutual close, requires server clearance. The escape withdrawal allows users to initiate a withdrawal without server approval, though the vault records a pending payout instead of immediate payment. A 24-hour challenge period ensures that the system can detect and prevent withdrawals from already-used states.
Additional controls include a pause switch that can halt new deposits and withdrawals, and an expiry mechanism that sends unclaimed funds to the treasury after 30 days. The system also uses Chainlink's ETH/USD price feed to stabilize billing rates during usage, though the underlying ETH balance remains subject to price fluctuations.