The Ethereum Foundation and the Open Anonymity Project launched zkAPI on Ethereum mainnet on October 1, 2026, allowing users to pay for API access without creating a trail linking payments to their identities. The system uses a smart contract vault (self-executing blockchain code) where users deposit ETH or USDC, with the funds converted into credits held by the vault as USDC credits. For an API request, including access to an AI model, a user generates a cryptographic proof authorizing payment. The service receives payment and returns the requested response, while the authorization is designed to be unlinkable to a particular deposit or identity. zkAPI uses Groth16 zero-knowledge proofs, Baby-JubJub commitments and a 32-level Merkle tree (a structure for proving membership without revealing a specific entry). Because the funds remain in Ethereum contracts rather than on a company server, users can withdraw independently without server cooperation. The project follows a February 11, 2026 research post by Vitalik Buterin and Davide Crapis, taking less than eight months from proposal to mainnet deployment. The Open Anonymity Project had received more than $100,000 in grants from the Ethereum Foundation and the Human Rights Foundation as of May 2026.