Ethereum Foundation launches zkAPI to let users pay for AI models without revealing identity

The Ethereum Foundation on Thursday launched zkAPI, a system that lets users pay for AI models and other metered APIs without revealing who they are, according to a blog post published Thursday.

The Foundation built zkAPI with the Open Anonymity (OA) Project, an open-source AI privacy effort, and it is live on Ethereum mainnet, the Foundation said in a blog post.

"Every AI API call today carries an identity," the post said. "Your API key points to an account, the account to a payment method, and every prompt you send joins the record attached to both. The provider can connect years of your usage into a single profile."

"It's like a generalization of OA unlinkable inference that also abstracts payments away," Ken Liu, a Stanford computer science PhD candidate who works on the Open Anonymity Project, said in an X post on Thursday afternoon. He added that "more infrastructure should exist where privacy and sovereignty is foundational and people are in control."

How zkAPI works

To use zkAPI, users must first deposit tokens such as ETH (ETH) or USDC into a vault contract on Ethereum, which records the user's balance as a private note, according to the post. To spend the tokens, software on the user's device generates a zero-knowledge proof which shows that its request is backed by a funded note, though it does not reveal which note or deposit funds it.