Ethereum Foundation Unveils zkAPI for Private AI Payments on Main Network

The Ethereum Foundation has launched zkAPI, a system for private AI payments on the main Ethereum network. This innovation allows users to request AI services without linking their identity to their requests. The project was built in collaboration with the Open Anonymity Project. The launch includes OA Chat, a browser-based private chatbot that can be used without installation.

According to the Ethereum Foundation, AI prompts contain sensitive information about users' health, finances, and doubts. The current AI services provide a record of users' thinking to whoever holds the billing relationship. The zkAPI system addresses this issue by using zero-knowledge proofs to verify the availability of funds without revealing the underlying details.

The user deposits credits, including ETH or USDC, into an Ethereum vault contract through a single transaction. The resulting balance becomes a private note that only the user can spend and cannot be traced to the deposit. The server checks the zero-knowledge proof and returns a temporary API key capped at a dollar amount.

The AI provider issues a signed usage receipt when the key expires. The user pays for actual usage rather than the key's spending cap. The AI provider sees the prompts, while the payment layer sees the spending, and neither can link the two. The documentation identifies OpenRouter as the provider behind the short-lived keys.

The zkAPI idea originated in a proposal by Davide Crapis and Vitalik Buterin posted on Ethereum Research in February. Crapis leads the Ethereum Foundation's dAI team, which aims to make Ethereum the preferred settlement and coordination layer for AIs. In May 2025, a federal court ordered OpenAI to preserve output logs, including chats users had deleted.