Ethereum Foundation launches zkAPI for private AI payments

The Ethereum Foundation and the Open Anonymity Project launched zkAPI on Ethereum mainnet on Oct. 1, letting users pay for metered AI services without linking their billing identity to requests, according to the Foundation’s announcement. The system uses zero-knowledge proofs to separate payment records from prompts sent to AI providers.

How does zkAPI separate payments from AI requests?

Users deposit funds, including ETH or USDC, into an Ethereum vault, where the balance is represented as a private note, the Foundation said. Software on the user’s device then proves to a zkAPI server that a note can cover a payment without revealing which deposit funded it.

After checking the proof, the server issues a temporary API key with a spending cap. The user sends prompts directly to the AI provider, and the server deducts the actual metered charge from the private balance when the key expires, according to the announcement.

The design publishes a one-way serial number, called a nullifier, for each spend to detect attempts to reuse the same balance. The Foundation said one authorization can cover a session of requests, with the provider recording usage in a signed receipt.

What can the provider and payment server still see?

The AI provider receives prompts and responses, while the zkAPI server sees that a valid payment exists and the session’s total spend, the Foundation said. The two sides are intended to lack the information needed to link a prompt to a payer.

zkAPI does not hide a user’s IP address or prompt contents, the Foundation cautioned. A stable IP address, request timing, personal details, writing style or reused conversation history could let parties correlate sessions.

The Foundation says the client supports standard OpenAI and Ollama APIs, so existing applications can connect through software running on the user’s device. Its announcement lists AI chat and agents as the first use case, with blockchain RPC queries and image generation among other possible metered services.

What earlier design does the launch implement?

zkAPI implements “ZK API Usage Credits,” a proposal by Ethereum Foundation dAI lead Davide Crapis and Ethereum co-founder Vitalik Buterin, according to the The Block’s report on the launch. The Foundation’s post identifies the Open Anonymity team as a contributor to the client, server and contracts.

The project is live on mainnet, and the Foundation says providers can integrate it by accepting proofs in place of API keys and settling signed usage receipts. The announcement also links to the project’s client, protocol and browser chat for developers and users.