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Ethereum Foundation launches zkAPI for private API payments

Ethereum Foundation and Open Anonymity launched zkAPI on Oct. 1, letting users fund AI API use on Ethereum without linking payments to prompts.

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The Ethereum Foundation and Open Anonymity Project launched zkAPI on Ethereum mainnet on Oct. 1, a system for paying for AI and other metered APIs without linking a user’s payment identity to their requests, according to the Ethereum Foundation announcement. The project uses zero-knowledge proofs to separate API spending from the deposit that funds it.

How does zkAPI separate payment from requests?

Users deposit ETH, USDC or other credits into a vault contract on Ethereum, where the balance is represented as a private note, the Foundation said. Software on the user’s device generates a proof that the note can cover a spend without identifying the note or its deposit.

A zkAPI server checks the proof and issues a temporary API key with a spending cap. The user sends prompts directly to the AI provider using that key; when it expires, a signed usage receipt lets the server deduct the actual cost from the private balance, according to the announcement.

What can the AI provider and payment server see?

The Foundation says the payment server can verify spending but does not see prompts, while the AI provider sees prompts but does not learn the billing identity behind the key. One authorization can cover a session rather than requiring a proof for every API call.

The tool also supports metered services beyond AI, including blockchain RPC queries, image generation and VPN bandwidth, the Foundation said. Its client exposes OpenAI and Ollama-compatible APIs, so existing apps can connect through a local gateway.

What privacy limits remain?

zkAPI hides the link between payment and API use; it does not make requests fully anonymous. The Foundation says providers still receive prompt content, and network metadata such as an IP address or request timing could help link sessions. Personal details or reused conversation history in prompts can also identify a user.

The system implements a design published on Ethereum Research by Ethereum Foundation researcher Davide Crapis and Vitalik Buterin, according to The Block’s report. The Foundation says zkAPI is live on mainnet.

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