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Ethereum Foundation launches private API payments with zkAPI

Ethereum launched zkAPI on Oct. 1, allowing users to pay for AI and other metered APIs with private credits while providers receive prompts without billing identities.

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The Ethereum Foundation and Open Anonymity Project launched zkAPI on Ethereum mainnet on Oct. 1, letting users pay for AI and other metered APIs without linking their billing identity to requests, the Foundation’s announcement said. Users deposit credits into an Ethereum vault and authorize spending with zero-knowledge proofs.

How does zkAPI separate payment from AI requests?

A user’s device proves to a zkAPI server that a private balance can cover usage, without identifying the deposit or payer, according to the Foundation. The server then issues a temporary API key with a spending cap; the user sends prompts directly to the AI provider, and the server later deducts the metered cost from the balance.

The Foundation says one authorization can cover a session rather than requiring a proof for every API call. The provider returns a signed receipt of the key’s usage, which the server uses to settle the charge. The initial release supports credits including ETH and USDC.

What can the provider and payment server still see?

The AI provider still sees prompts and responses, while zkAPI’s payment server sees payment activity and the session’s total spend, the Foundation said. The design aims to prevent either side from linking the prompts to the user’s billing identity.

That protection does not hide network details. The Foundation says a gateway may correlate requests from a stable IP address, and providers may reconnect sessions based on prompt contents, such as repeated personal details or conversation history.

What is live on mainnet?

The Foundation said the system was built with the Open Anonymity Project and is live on Ethereum mainnet. Its announcement describes zkAPI as an implementation of “ZK API usage credits,” a design published on Ethereum Research by Ethereum Foundation researcher Davide Crapis and Ethereum co-founder Vitalik Buterin.

The project also lists blockchain RPC, image and video generation, VPN bandwidth and machine-to-machine services as potential metered uses. The Block’s report on the launch likewise notes the system’s limits around IP addresses and prompt content.

Sources