The Ethereum Foundation and the Open Anonymity Project launched zkAPI on Ethereum mainnet to let users pay for AI models and other metered APIs without linking payments to identities. The system went live on October 1, 2026, and centers on a smart-contract vault where users deposit ETH or USDC; those deposits become credits that the vault treats as private balances. To call an API, client software generates a zero-knowledge proof showing a request is backed by funds without revealing which deposit or which user provided them. A zkAPI server verifies the proof, issues a temporary API key with a quota, and the user sends requests directly to the AI provider; after usage the server deducts fees from the private balance and publishes a serial nullifier to prevent double-spend attempts.
Under the hood zkAPI relies on standard ZK building blocks: reports cite Groth16 proofs, Baby-JubJub commitments and a 32-level Merkle tree, while other descriptions mention BN254 and Poseidon. The Ethereum network records on-chain operations such as deposits, settlements and withdrawals but cannot learn which services specific funds paid for; users can withdraw funds directly from chain contracts if a server stops cooperating. The design implements the “ZK API Usage Credits” scheme that Vitalik Buterin and Davide Crapis published on Feb. 11, 2026, and was built by the Foundation’s dAI team led by Davide Crapis with a blog post by Vittorio Rivabella.
The launch frames zkAPI initially for AI inference because prompts can contain sensitive data like health or finances, but also lists other usage-based billing cases such as blockchain RPC, image and video generation, VPN bandwidth and machine-to-machine payments between AI agents. The project is described as experimental and has limitations: it does not provide network-level anonymity (stable IPs can correlate sessions) and prompt content or writing style can re-link sessions. The initiative follows prior dAI work, including the ERC-8004 standard, and Open Anonymity had received over $100,000 in grants from the Ethereum Foundation and the Human Rights Foundation as of May 2026.