Ethereum Foundation launches zkAPI for private AI payments

What happened

The Ethereum Foundation launched zkAPI, which lets people pay for AI models and other metered APIs without revealing their identity. The system is live on Ethereum mainnet and was built with the Open Anonymity Project. Users deposit tokens such as ETH or USDC into a vault contract on Ethereum, which records the balance as a private note. Software on the user's device then generates a zero-knowledge proof showing the request is backed by a funded note. A zkAPI server checks the proof and issues a temporary API key with a spending cap. A serial number called a nullifier is published each time a user pays for AI usage.

The client exposes the standard OpenAI and Ollama APIs on the user's own machine, so existing apps, editors and chat clients work by pointing them at localhost. 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. Alongside the launch comes OA Chat, a browser-based private chatbot that needs no installation, and the code is open on GitHub. The blog post announcing zkAPI was written by Vittorio Rivabella of the dAI team.

Why it matters

The Foundation argues that prompts are personal. People ask AI models about their health, their finances and their doubts, and under the current model using AI means handing a running transcript of your thinking to whoever holds the billing relationship. The concern is not abstract. 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.

zkAPI separates payment from identity. The provider sees what you asked, the payment layer sees what you spent, and neither can link the two. The same plumbing could cover other metered services, including blockchain data queries, image and video generation, VPNs and payments between machines. The post lists AI chat and agents as the first use case.

Background

The idea comes from a proposal Davide Crapis and Vitalik Buterin posted on Ethereum Research in February. zkAPI implements "ZK API Usage Credits," a design the two published on the Ethereum Research forum on Feb. 11. Crapis leads the Ethereum Foundation's dAI team, which the Foundation formed in September 2025 to improve Ethereum's capabilities as a settlement and coordination layer for AI.

The team also developed ERC-8004, a standard for AI agent identity that launched on mainnet in January. 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. On February 10, Buterin laid out an Ethereum-AI roadmap that included zero-knowledge payments for private API use. In April, he showed another path: running an open-source model locally on his own Nvidia 5090 graphics card.

What is still unclear

• The zkAPI system does not provide network anonymity. The gateway can potentially correlate requests sent from a stable IP address, and users seeking stronger privacy may route traffic through Tor.
• Sessions can also be re-linked through the content of prompts, such as personal details, writing style or conversation history.
• The zkAPI project's GitHub repository describes the protocol as experimental.

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