Key highlights:
A new system, zkAPI, has been introduced by the Ethereum Foundation on the Ethereum mainnet. With this new method, users can pay for AI models and other metered services anonymously. This was developed as a collaboration project between the Ethereum Foundation and the Open Anonymity Project.
Before now, users were paying for services from AI using either a credit card or an API key associated with their account. This method was considered highly risky because every request made by the user can be easily traced to their financial details.
How Ethereum’s zkAPI works
The process was simplified for users by the developers. Users can put tokens like ETH or USDC in a vault contract on Ethereum. Those funds are then changed to a private spendable balance through a cryptographic note. These notes represent money that can be spent by the user freely without being identified.
The next step is initiating the payment process. A zero-knowledge proof is created through locally running software, while keeping the details of the deposit private. This proof can apply to either one transaction or a whole usage session, according to the Ethereum Foundation.
After creating the proof, a zkAPI server verifies it and generates an API key with the spending limit set. The user can then send the prompt to the AI provider with this temporary key. The system will charge the balance from the user’s private balance when the key expires.
To stop people from spending the same funds twice, the system uses a nullifier, which is a unique serial number generated each time a payment goes through. If a user tries to reuse funds that have been spent, the system catches the duplicate immediately.
Built to work with tools people already use
One of the practical design decisions made for zkAPI is that developers will not need to rebuild their AI tools from scratch. The system offers access to standard APIs similar to OpenAI. This makes it possible for current applications, code editors, among others to connect to the system via localhost.
The Ethereum Foundation expects AI chat and AI agents to be among the first real-world use cases for this solution. They also highlighted generation of images and videos, and even payments for the bandwidth of VPNs could use the tool.
The product was developed after previous research done in February. Researchers from the Ethereum Foundation and co-founder of Ethereum named Vitalik Buterin submitted a proposal named ZK API Usage Credits. This product is a result of the proposal.
The Foundation formed its dAI research team in September 2025, specifically to help position Ethereum as a settlement and coordination layer for AI related activities.
Source:: Ethereum's zkAPI Brings Privacy-Preserving API Payments to Mainnet