Ethereum Foundation launches zkAPI for private payments to AI models

The Ethereum Foundation launched zkAPI on Thursday, letting users pay for AI models and other metered APIs without revealing their identity, according to its blog post. The Foundation built zkAPI with the Open Anonymity Project, an open-source AI privacy effort, and said the system is live on Ethereum mainnet. The Foundation said conventional AI API keys connect an account, payment method and prompts, allowing providers to build a profile of a user's activity. Users must first deposit tokens such as ETH or USDC into a vault contract on Ethereum, which records each balance as a private note, according to the post. Software on the user's device then generates a zero-knowledge proof that a funded note backs a request 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 and the key directly to an AI model provider. When the key expires, the server deducts the usage from the user's private balance. Each payment publishes a serial number called a nullifier; a duplicate nullifier exposes an attempt to spend the same balance twice, according to the post. The Foundation said the client exposes standard OpenAI and Ollama APIs locally so existing apps, editors and chat clients can use it. The post lists AI chat and agents as the first use case. It also lists blockchain RPC queries, image and video generation, VPN bandwidth and payments between AI agents as potential applications. The post said zkAPI does not provide network anonymity because a gateway may correlate requests from a stable IP address. Users seeking stronger privacy may route traffic through Tor, according to the post. Prompt details, writing style or conversation history can also link sessions. The project's GitHub repository describes the protocol as experimental. zkAPI implements a design called ZK API Usage Credits, which Ethereum co-founder Vitalik Buterin and Ethereum Foundation dAI lead Davide Crapis published on the Ethereum Research forum on February 11. The Foundation formed its dAI team 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. Buterin discussed cryptographic payment mechanisms for AI services in a February post about his near-term vision for Ethereum and AI.