Ethereum Foundation launches zkAPI for private AI payments on main network

The Ethereum Foundation announced that zkAPI is live on Ethereum's main network, allowing people to pay for AI services without linking their identity to their requests. The project was built with the Open Anonymity Project. The launch includes OA Chat, a browser-based private chatbot that requires no installation. The project's code is open on GitHub. The repository labels the protocol experimental and does not list a formal audit.

The Ethereum Foundation argued that AI prompts contain personal information about users' health, finances and doubts. The Foundation argued that current AI services give whoever holds the billing relationship a continuing record of users' thinking. The Foundation said users deposit credits, including ETH or USDC, into an Ethereum vault contract through one ordinary transaction. The Foundation said the resulting balance becomes a private note that only the user can spend and nobody can trace to the deposit.

Software on the user's device builds a zero-knowledge proof for each AI request, proving sufficient funds are available and have not already been spent. A zero-knowledge proof establishes a fact without revealing its underlying details. The server checks the proof and returns a temporary API key capped at a dollar amount. The API key remains only in the device's memory. Requests reach the AI provider with the key but without a name or payment details.

The provider issues a signed usage receipt when the key expires. The user pays for actual usage rather than the key's spending cap. The AI provider sees the prompts, while the payment layer sees the spending, and neither can link the two. The documentation identifies OpenRouter as the provider behind the short-lived keys. OpenRouter gives access to hundreds of AI models through one connection. Any app using the OpenAI format can connect by pointing to a local address.

In May 2025, a federal court ordered OpenAI to preserve output logs, including chats users had deleted. The order arose from a copyright lawsuit brought by The New York Times and other publishers.

The zkAPI idea originated in a proposal Davide Crapis and Vitalik Buterin posted on Ethereum Research in February. Crapis leads the Ethereum Foundation's dAI team, which aims to make Ethereum the preferred settlement and coordination layer for AIs. In August 2025, Crapis and Marco De Rossi proposed ERC-8004, a standard allowing autonomous AI agents to discover each other, verify identity and transact. Crapis predicted that machines would generate most Ethereum traffic within three to five years.

Buterin outlined an Ethereum-AI roadmap on February 10 that included zero-knowledge payments for private API use. In April, Buterin demonstrated running an open-source model locally on an Nvidia 5090 graphics card instead of using cloud services. Local models keep users' data at home. However, zkAPI addresses cases where prompts still travel to another party's servers.

The launch post says the same infrastructure could support other metered services, including blockchain data queries, image and video generation, VPNs and payments between machines. Providers integrating directly would have to accept a proof instead of an API key and settle signed usage receipts.