The Ethereum Foundation has deployed zkAPI on Ethereum mainnet in collaboration with the Open Anonymity Project, enabling privacy-preserving payments for AI API services. The protocol uses zero-knowledge proofs to decouple payment identity from service requests, allowing users to deposit ETH or USDC into a vault and authorize usage quotas without revealing their identity to providers or payment processors. zkAPI generates temporary API keys after verifying sufficient funds via cryptographic proofs, ensuring service providers see request content but not payer identity, while payment processors only view spend amounts without linking them to specific users. Built on Groth16, BN254, Poseidon, and Merkle trees, the system records only deposits, settlements, and withdrawals on-chain, keeping individual service payments private. Initially targeting AI inference to protect sensitive prompts involving health or financial data, zkAPI also supports usage-based billing for blockchain RPC and media generation. Users retain custody with direct on-chain withdrawal capabilities if servers cease operation.