zkAPI is live on Ethereum mainnet as a payment layer for metered APIs, not as a slogan about private AI. On 1 October 2026 the Ethereum Foundation published the launch note: you deposit credits (ETH, USDC, and similar) into an onchain vault once, then authorize bounded usage with zero-knowledge proofs instead of an identity. The Open Anonymity Project built it with the Foundation. The post says it runs on Ethereum Mainnet today.
I care about shipped mechanics. A vault you can exit without the server’s honesty is more interesting than another “privacy roadmap.” Our CoinGecko snapshot at 2026-10-01T23:55:55+00:00 showed ether (ETH) at $2,704.91, up 0.73% over 24 hours, with bitcoin (BTC) at $84,810. That tape is mid-$80k chop, not a reason to ignore a live contract on Ethereum’s history as a settlement layer.
Show me the fee path, not the pitch deck. zkAPI still needs a real Ethereum transaction to fund the note. It does not make gas fees disappear.
What happened
The Foundation post is dated 1 October 2026, by Vittorio Rivabella of the dAI team. The short version is blunt. Every ordinary AI API call today carries an identity: an API key points to an account, the account to a payment method, and prompts pile up on that record. zkAPI splits the payment path from the conversation path.
You deposit into a vault smart contract on Ethereum. After that, the balance lives as a private note. Software on your machine produces a Groth16 proof on the BN254 curve that a funded note covers this spend and has not been spent before. The server checks the proof off-chain and mints a short-lived, dollar-capped API key that exists only in device memory. Prompts then go to the provider with that key. When the key expires, a signed usage receipt deducts metered usage from the note rather than the reserved cap.
The post names the live mainnet vault as ZkApiVault at 0x4386fdbda35d995beb3bf8625118ec5982ec81fe, described as holding USDC credits. A Sepolia copy sits at 0x49fa19f9bdece7a48ebc7749fd69ad40f577590f. The client, server, and browser SDK are in the ethereum/zkapi GitHub repository. The local client is meant to speak OpenAI and Ollama APIs on localhost, so existing apps can point at it.
Cryptography details in the same post: Poseidon hashes for commitments and nullifiers, a Merkle tree 32 levels deep, and a duplicate nullifier if someone tries to spend the same note twice. The vault contract verifies proofs at deposit, close, and escape, so an exit is not supposed to depend on the server staying honest.
Context
This is not a brand-new research sketch. On 11 February 2026, Davide Crapis posted “ZK API Usage Credits: LLMs and Beyond” on Ethresear.ch, credited to Crapis and Vitalik Buterin. That thread framed the same three-way bind: privacy, security, and efficiency for metered APIs, especially LLM prompts. The October post presents zkAPI as the working implementation of that design, with Open Anonymity helping turn it into client, server, and contracts.
The Foundation is also honest about what zkAPI does not hide. The payment layer should not learn who you are or what you asked. The AI provider still sees prompts and responses. Ethereum still sees deposits, closes, and withdrawals. A stable IP can still correlate sessions. Reused writing style or pasted documents can still fingerprint you to the model host. There is a simpler proxy mode where the zkAPI server relays traffic and therefore sees it. The runtime-key mode exists so the payment intermediary does not.
Fee context still matters, because the first hop is an onchain deposit. DefiLlama’s Ethereum fee overview (api.llama.fi/overview/fees/ethereum), pulled 2026-10-02T00:17:00Z, showed about $12.45 million of fees in the prior 24 hours, down 5.68% versus the previous 24-hour bucket. Ethereum chain TVL on DefiLlama’s chains endpoint at the same pull was about $53.68 billion. That is a large, working fee market. zkAPI rides it. It does not replace it.
The same snapshot put global crypto market cap near $2.91 trillion, with bitcoin dominance about 58.59%. Ether was not in a blow-off. Solana printed $118.38. None of that prices a privacy API. It does tell you the chain zkAPI settled on is still the one collecting most DeFi fees.
For more on how we timestamp tape like this, see how to read a crypto market snapshot. Related Ethereum news will keep sitting next to fee prints, not next to slogans.
Our read
My stance: treat zkAPI as a live Ethereum vault plus a local API shim, not as “private ChatGPT.” The interesting claim is mechanical. Credits sit in a contract you can close onchain. Spend authorization is a proof plus a nullifier, not an email. Session keys are capped and short-lived. If operators skip the runtime-key path and run the relay, they re-centralize content in the payment server. That would be old web2 with extra Groth16.
I also do not read “holding USDC credits” as a TVL trophy. The Foundation did not publish a deposit total in the 1 October post. I did not invent one. A vault can be live and still empty enough that nobody should market it as a liquidity event.
Falsifiable claim: if by 2026-10-16 23:59 UTC the Ethereum Foundation updates or retracts the 1 October post so that zkAPI is no longer described as live on Ethereum Mainnet, or so that ZkApiVault at 0x4386fdbda35d995beb3bf8625118ec5982ec81fe is no longer listed as the live mainnet vault, then this read is wrong.
What to watch
Watch whether providers actually accept proofs and signed receipts instead of account API keys. The post says pricing and rate limits stay as they are. Until a named inference host says it settles that way in production, the mainnet vault is a user-side credit system pointing at OA Chat and localhost shims.
Watch the two failure modes the Foundation already listed: IP correlation and prompt fingerprinting. If the public docs start claiming network anonymity they did not ship, that is a different product.
Watch GitHub ethereum/zkapi for whether the client stays OpenAI-compatible and whether the vault addresses in the README still match the blog. A silent address change without a post update would be a red flag for anyone who deposited.
Watch Ethereum fees on the same DefiLlama feed. If deposit costs spike while AI metering stays cheap in dollars, zkAPI’s “one ordinary transaction” setup cost becomes the real UX. If fees stay in this quiet band, the bottleneck is provider integration, not gas.