The Ethereum Foundation and the Open Anonymity Project launched zkAPI on the Ethereum mainnet on October 1, introducing a system that allows users to prepay for artificial intelligence services using zero-knowledge proofs without revealing their identities.
According to the announcement, the protocol is designed to separate payment from identity. Users deposit funds such as ETH or USDC into an Ethereum vault contract via a standard transaction. Afterward, the balance is held as a private note, functioning as digital cash that can be spent anonymously.
The system operates by having software on the user's device generate a zero-knowledge proof for each AI query. This cryptographic receipt verifies that the user has sufficient funds and has not previously spent them, without revealing the underlying details. Upon verifying the proof, the server issues a temporary, memory-based API key capped at a specific dollar amount. Requests are then sent to the AI provider using only the key, preventing the provider from linking the payment details to the prompts.
When the temporary key expires, the provider issues a signed usage receipt, and the user is charged only for the actual amount consumed. Documentation points to OpenRouter as the AI provider currently behind the keys, allowing access to numerous models through a single connection.
The design originates from a February proposal on Ethereum Research authored by Vitalik Buterin and Davide Crapis, who leads the Ethereum Foundation's dAI team. Accompanying the launch is OA Chat, a browser-based private chatbot that requires no installation, with code available publicly on GitHub.
The project repository currently labels the protocol as experimental and does not cite a formal audit. The underlying technology could potentially expand to cover other metered services, including blockchain data queries, video and image generation, VPNs, and machine-to-machine payments.
