Ethereum Foundation Launches zkAPI for Private AI Payments

What it claims

zkAPI is live on Ethereum mainnet. It is the first working build of the Crapis/Buterin Ethereum Research design. The page's core claim is a split in what each party learns. The payment server never sees prompts. The AI provider never sees who is paying. The ZK proof shows that you paid without revealing which deposit in the vault is yours, so your anonymity comes from the pool of other depositors.

How it works

flowchart LR
  U[User device] -->|one-time USDC deposit| V[Vault contract, mainnet]
  U -->|ZK proof of payment| P[Payment server]
  P -->|short-lived, spend-capped key| U
  U -->|key + prompt, IP visible| A[AI / API provider]
  V -.->|withdraw if servers down| U

1. Fund the on-chain vault once. The live vault holds USDC.
2. Your device generates a proof that you deposited, without revealing which deposit.
3. The payment server checks the proof and issues a short-lived key with a spending cap. It sees no prompts.
4. You call the provider with that key. The provider sees the key and your traffic, but no billing identity.

The page names metered uses beyond AI: RPC queries, image generation, VPN bandwidth, and agent-to-agent payments, all without accounts.

How to use it

The page names the access paths: a local client that exposes OpenAI- and Ollama-compatible interfaces, and the in-browser OA Chat. It gives no install commands, repository link, contract address, fees, or cap sizes. You will need to find those at the source before adopting it.

Limits

• Only the payment link is hidden. Providers still see your IP address and prompt content. The team suggests routing through Tor.
• Prompt content can re-link sessions. The page warns that reused context, such as personal details or a recognisable writing style, can tie separate sessions back together even without a billing link. Apps that inject stable user profiles or system context into every request would undo the unlinkability. This failure mode is not in the existing summary.
• Anonymity depends on the vault's depositor pool. The proof hides which deposit is yours among all deposits. The page gives no figures on vault size or usage.
• The source is a news brief. Bankless calls zkAPI "an early, partial fix." There is no technical spec, threat model, audit status, or performance data on the page.