Ethereum Foundation launches zkAPI for private AI payments on mainnet

The Ethereum Foundation has put zkAPI live on Ethereum's main network, a system that lets people pay for AI services without tying their identity to what they ask, according to the Ethereum Foundation's announcement.

“Prompts are personal. People ask AI models about their health, their finances, their doubts. Under the current model, using AI means handing a running transcript of your thinking to whoever holds the billing relationship,” the Ethereum Foundation argued.

“zkAPI separates payment from identity,” the Foundation continued. “You deposit credits (ETH, USDC, etc.) into a vault contract on Ethereum, one ordinary transaction. From then on, your balance exists as a private note: digital cash that only you can spend and that nobody can trace back to the deposit.”

It was built with the Open Anonymity Project. Alongside the launch comes OA Chat, a browser-based private chatbot that needs no installation, and the code is open on GitHub.

The concern over privacy in the AI space isn't an abstract one. In May 2025, a federal court ordered OpenAI to preserve its output logs, including chats users had deleted, in a copyright lawsuit brought by The New York Times and other publishers.

With this implementation, every time you want to ask an AI something, software on your device builds a zero-knowledge proof—a mathematical receipt that proves a fact without showing the details behind it. This one proves you have enough funds and haven't already spent them.

The server checks the proof and hands back a temporary API key, which is basically a password that lets software talk to an AI service. The key is capped at a dollar amount and lives only in your device's memory.

Your requests then go to the AI provider with that key and nothing else. No name, no payment details.

When the key expires, the provider issues a signed usage receipt and you're charged for what you actually used, not the cap. The provider sees what you asked, the payment layer sees what you spent, and neither can link the two.

The project's documentation describes short-lived keys that work with OpenRouter, a service that gives access to hundreds of AI models through one connection. Any app that speaks the OpenAI format can plug in by pointing at a local address.

The idea comes from a proposal Davide Crapis and Vitalik Buterin posted on Ethereum Research in February. Crapis leads the foundation's dAI team, which aims to make Ethereum the preferred settlement and coordination layer for AIs.

He had already pitched Ethereum as plumbing for software agents. In August 2025, Crapis and Marco De Rossi proposed the ERC-8004 standard, a shared rulebook that lets autonomous AI agents find each other, verify identity and transact. Crapis predicted most Ethereum traffic would come from machines within three to five years.

Buterin ran the same thread. On February 10, he had laid out an Ethereum-AI roadmap that included zero-knowledge payments for private API use.

In April, he showed the other path: running an open-source model locally on his own Nvidia 5090 graphics card instead of feeding his life to cloud services. Local models keep your data at home. zkAPI covers the case where your prompts still travel to someone else's servers.

The same plumbing could cover other metered services, per the post: blockchain data queries, image and video generation, VPNs, and payments between machines. Providers would have to accept a proof instead of an API key and settle signed usage receipts to integrate directly.

The repository itself labels the protocol experimental and does not list a formal audit.