Ethereum Mainnet Gets zkAPI: Private Metered Payments Without Identity Exposure

The Ethereum Foundation and the Open Anonymity Project have quietly launched a new payment system on the Ethereum mainnet, called zkAPI, designed to solve the problem of identity exposure in metered online services. This issue arises when users pay for services like AI models or cloud APIs, as their identity is often linked to each request, potentially revealing sensitive information.

zkAPI allows users to make private metered API payments without linking individual requests to a durable billing account. This is achieved through a system where users deposit ETH or USDC into a vault contract, creating a private 'note' that functions like digital cash. Zero-knowledge proofs then confirm a payment is valid without revealing who made it or what it paid for.

The system relies on cryptographic techniques, including Merkle trees, nullifiers, and off-chain verification, to ensure that payments remain unlinkable on-chain. While zkAPI does not hide request content or network metadata, it does protect the billing relationship from being correlated with individual requests or user identities.