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How zkAPI works
The direct flow combines a private balance, a locally created proof, a limited API lease and usage settlement. The proof supports the service’s authorization decision, but it does not replace the lease or the system’s separate vault operations.
- Fund the vault. A user deposits funds into an Ethereum vault. The protocol represents the balance as a private note rather than exposing the note’s identity in each later proof.
- Create a proof in the client. The client uses the note’s secret information to prove that it can cover an allowed spend. Current zkAPI v2 documentation says the browser SDK runs the prover in WebAssembly (WASM), so proof creation occurs in the browser.
- Obtain an API lease. The server verifies the proof and checks the relevant protocol state, including protections against spending the same note twice. If the checks pass, it can issue a short-lived API key with a spending cap. This is the service’s bounded permission to use the API—not an instruction that the proof independently sends to Ethereum.
- Make API requests. In the direct lease approach, the client sends prompts to the API provider. The provider records metered use in a signed receipt; the server uses measured usage to settle against the private balance.
- Withdraw or recover funds. The project documentation describes on-chain vault withdrawals and escape or challenge mechanisms. These are vault operations, separate from proof verification and API access.
The Ethereum Foundation’s October 1, 2026 launch description also outlines a proxy mode, in which zkAPI relays requests. Unlike the direct flow, a relay handling the request can see its traffic.
What the proof does—and what it does not do
A zero-knowledge proof lets a prover establish that a statement is valid without revealing the private information used to establish it. Ethereum.org describes completeness, soundness and zero-knowledge as defining properties of zero-knowledge proofs. In zkAPI, the relevant statement concerns membership of a private note and whether it covers the permitted spend; a nullifier helps prevent the same note from being spent again.
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Successful verification tells the service that the proposed spend satisfies the protocol’s rules. It does not, by itself, move ETH, make an API provider accept a request or settle usage. The lease is the service’s API permission, usage is measured and settled separately, and deposits or withdrawals involve separate on-chain vault transactions.
One limited analogy is a verifiable ticket showing that a capped charge can be covered: the proof supports the ticket check, the lease grants API access, and the vault manages funds and withdrawals. The analogy does not capture every protocol detail.
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Who can see what
zkAPI is intended to separate the billing link from API activity; it does not conceal every part of using an API. The distinctions below describe the direct flow. In proxy mode, the relay’s visibility differs because it handles the requests.
| Party | What it can see | What remains concealed or limited |
|---|---|---|
| zkAPI authorization server | Whether a proof is valid, plus session spend and settlement information. | In the described direct design, it does not receive prompts and is not meant to learn which private note or deposit authorized the spend. |
| Inference provider | Prompts, responses and ordinary request context. | The billing identity behind the lease is intended to remain separate. Repeated context or writing patterns may still make sessions correlatable. |
| Ethereum public chain | Vault deposits, closes and withdrawals. | The launch description says the chain does not show what a balance paid for; the funding and exit transactions themselves are public. |
| Network observers or services | IP addresses and timing may remain observable. | zkAPI is not network anonymity. The Foundation suggests Tor with a fresh circuit as an additional layer for users who need it. |
In short, the privacy claim concerns the link between a payment identity or deposit and API use—not secrecy from the inference provider about the content it processes, or anonymity at the network layer. Content patterns can also correlate sessions even when the billing link is concealed.
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Which assets and providers does zkAPI support?
The answer depends on which description and version you mean. The Ethereum Foundation’s launch post, published October 1, 2026, describes ETH, USDC and other credits being deposited in a vault, and says the vault holds USDC. The current Open Anonymity Project protocol documentation, accessed October 2, 2026, describes v2 as funded with native ETH and its leases as being for OpenRouter. These descriptions have different dates and scopes; they should not be combined into a single timeless list of supported assets or providers.
For the current v2 documentation’s stated scope, native ETH funding and OpenRouter leases are the specific details given. The launch post presents a broader vision of metered services, not evidence that every API provider already supports zkAPI.
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Cryptography, setup and security limits
The project documentation identifies the current protocol as v2, circuit revision zkapi-v2-note-bound-v1. Its stated components include Groth16 over BN254, Poseidon hashes, Baby-JubJub commitments, Schnorr signatures and a 32-level Merkle tree. The API reference gives an encoded proof size of 256 bytes; it does not state a publication date for that figure.
These are project-stated engineering details, not independent security findings. The project describes the protocol as experimental, says its checked-in proving keys use a single-party setup without a multiparty ceremony, and states that the construction is not post-quantum. The reviewed project materials do not establish an independent audit result. They also say that the circuit, proving and verifying artifacts, vault deployment and server keys must match, making correct configuration part of the system’s operational requirements.
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What zkAPI might be used for
The Ethereum Foundation lists AI chat and agents, blockchain RPC, image and video generation, VPNs or bandwidth, and machine-to-machine services as possible uses for metered payments. These are proposed application areas, not proof of broad third-party adoption. The cited materials do not establish user counts, independent performance benchmarks, cost savings or security benchmarks.
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