Ethereum's zkAPI Brings Private Payments to Metered APIs

zkAPI is an Ethereum-based system that allows users to make private payments for metered APIs without revealing their identity. The system, introduced by the Ethereum Foundation on October 1, 2026, uses Ethereum deposits as a form of credit for API payments.

The process works as follows: users deposit assets such as ETH or USDC into a vault contract on Ethereum, which creates a private note that cannot be traced back to the original deposit. When making a request, software on the user's device generates a zero-knowledge proof showing two things: that the server has checked the proof without learning the user's identity or the original deposit.

The server then creates a short-lived API key capped in dollars, which stays in the user's device's memory. Once it expires, the AI provider records actual usage in a signed receipt, and the server deducts that amount from the user's private balance. The final charge is based on metered use, not the full amount reserved at the start.

While zkAPI does provide privacy for API payments, it does not make every use of Ethereum private. The vault contract still records deposits, closes, and withdrawals, and the provider can see the contents of each request, along with network metadata such as IP address.