--- title: Introducing zkAPI: private usage credits for any API description: zkAPI is a new protocol from the Open Anonymity Project and the Ethereum Foundation that lets users pay for metered APIs, especially AI inference, without... canonical: https://daily.dev/posts/introducing-zkapi-private-usage-credits-for-any-api-hg86btyxu twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Introducing zkAPI: private usage credits for any API | daily.dev og:description: zkAPI is a new protocol from the Open Anonymity Project and the Ethereum Foundation that lets users pay for metered APIs, especially AI inference, without... og:url: https://daily.dev/posts/introducing-zkapi-private-usage-credits-for-any-api-hg86btyxu og:image: https://api.daily.dev/og/posts/HG86BtyxU.png og:image:alt: Introducing zkAPI: private usage credits for any API og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Introducing zkAPI: private usage credits for any API **[Ethereum](https://daily.dev/sources/ethereum)** · 6 min read · 0 upvotes · 0 comments ## Summary zkAPI is a new protocol from the Open Anonymity Project and the Ethereum Foundation that lets users pay for metered APIs, especially AI inference, without linking payment identity to usage. Users deposit ETH or USDC into an Ethereum vault contract, then authorize spending via zero-knowledge proofs instead of API keys tied to accounts. A local client mints short-lived, capped API keys, so the payment server never sees prompts and the AI provider never learns the billing identity. The system uses Groth16 proofs on BN254, Poseidon hashing, and a 32-level Merkle tree of commitments and nullifiers to prevent double-spending while preserving unlinkability. It runs on Ethereum Mainnet now, exposes standard OpenAI and Ollama-compatible APIs locally, and is designed to generalize to RPC calls, image/video generation, VPNs, and machine-to-machine payments. Limitations remain around network-level correlation (IP, timing) and content-level fingerprinting through prompt style or reused context. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What is zkAPI and how does it let you pay for AI API usage without revealing your identity? zkAPI is a protocol built by the Open Anonymity Project and the Ethereum Foundation that separates payment from identity for metered APIs. Users deposit ETH or USDC into an Ethereum vault contract once, then authorize spending with zero-knowledge proofs instead of an API key tied to an account. The payment server verifies a valid note was spent without learning which deposit or person it came from, while the AI provider sees prompts but never the billing identity. It runs live on Ethereum Mainnet. _Developers weighing privacy-preserving payment layers for AI APIs can follow projects like this on daily.dev._ ### What cryptography does zkAPI use to prevent double-spending while staying private? zkAPI proves spends using Groth16 zero-knowledge proofs on the BN254 curve, hashes commitments and nullifiers with the Poseidon hash function, and stores deposit commitments in a Merkle tree 32 levels deep. Each spend publishes a one-way nullifier derived from the note's secret; spending within balance stays unlinkable, while reusing the same note produces a duplicate nullifier that exposes the double-spend attempt without revealing anything else. _Anyone building zero-knowledge payment systems can track implementation details like this via daily.dev._ ### What are the privacy limitations of zkAPI's anonymous API payment system? zkAPI hides the payment link but not everything: a gateway can potentially correlate requests from a stable IP address, so users seeking stronger anonymity should route through Tor with a fresh circuit per session. On the content side, an inference provider can re-link sessions if prompts share personal details, writing style, or reused conversation history, since shared prompt contents act as fingerprints even when payment is anonymous. _Engineers evaluating privacy trade-offs in AI infrastructure can keep up with findings like these on daily.dev._ ## Similar posts on daily.dev - [Integrating ZK-Proofs and Privacy in Solidity Smart Contracts](https://daily.dev/posts/integrating-zk-proofs-and-privacy-in-solidity-smart-contracts-l6tejg0wj) · Coins Bench · 1 upvotes · 0 comments - [Enterprise Smart Contracts Have a Cryptography Problem. EY Just Built a Way Around It](https://daily.dev/posts/enterprise-smart-contracts-have-a-cryptography-problem-ey-just-built-a-way-around-it-czjjr0jyr) · DevOps.com · 0 upvotes · 0 comments - [Zero-Knowledge Proofs for Privacy-Preserving Context Validation](https://daily.dev/posts/zero-knowledge-proofs-for-privacy-preserving-context-validation-ow9k48ypx) · Security Boulevard · 0 upvotes · 0 comments - [foojay – a place for friends of OpenJDK](https://daily.dev/posts/foojay-a-place-for-friends-of-openjdk-daxnzhtrp) · Foojay.io · 1 upvotes · 0 comments - [zkLogin: when ZKP is not enough](https://daily.dev/posts/zklogin-when-zkp-is-not-enough-tvrkv8oi8) · Brave · 0 upvotes · 0 comments --- Tags: [#architecture](https://daily.dev/tags/architecture), [#privacy](https://daily.dev/tags/privacy), [#cryptography](https://daily.dev/tags/cryptography), [#ethereum](https://daily.dev/tags/ethereum), [#zero-knowledge-proofs](https://daily.dev/tags/zero-knowledge-proofs) [View this post on daily.dev](https://daily.dev/posts/introducing-zkapi-private-usage-credits-for-any-api-hg86btyxu) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Introducing zkAPI: private usage credits for any API","url":"https://daily.dev/posts/introducing-zkapi-private-usage-credits-for-any-api-hg86btyxu","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/introducing-zkapi-private-usage-credits-for-any-api-hg86btyxu"},"datePublished":"2026-10-01T19:05:12.233Z","dateModified":"2026-10-01T19:09:23.530Z","description":"zkAPI is a new protocol from the Open Anonymity Project and the Ethereum Foundation that lets users pay for metered APIs, especially AI inference, without...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/bf3eee7b77494462c9a382f9797a4ffd?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/bf3eee7b77494462c9a382f9797a4ffd?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Ethereum","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Ethereum","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/881328ee52904833bc407acdbad603ee","url":"https://daily.dev/sources/ethereum"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/introducing-zkapi-private-usage-credits-for-any-api-hg86btyxu","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"architecture,privacy,cryptography,ethereum,zero-knowledge-proofs","timeRequired":"PT6M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Ethereum","item":"https://daily.dev/sources/ethereum"},{"@type":"ListItem","position":3,"name":"Introducing zkAPI: private usage credits for any API"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/introducing-zkapi-private-usage-credits-for-any-api-hg86btyxu#faq","mainEntity":[{"@type":"Question","name":"What is zkAPI and how does it let you pay for AI API usage without revealing your identity?","acceptedAnswer":{"@type":"Answer","text":"zkAPI is a protocol built by the Open Anonymity Project and the Ethereum Foundation that separates payment from identity for metered APIs. Users deposit ETH or USDC into an Ethereum vault contract once, then authorize spending with zero-knowledge proofs instead of an API key tied to an account. The payment server verifies a valid note was spent without learning which deposit or person it came from, while the AI provider sees prompts but never the billing identity. It runs live on Ethereum Mainnet. Developers weighing privacy-preserving payment layers for AI APIs can follow projects like this on daily.dev."}},{"@type":"Question","name":"What cryptography does zkAPI use to prevent double-spending while staying private?","acceptedAnswer":{"@type":"Answer","text":"zkAPI proves spends using Groth16 zero-knowledge proofs on the BN254 curve, hashes commitments and nullifiers with the Poseidon hash function, and stores deposit commitments in a Merkle tree 32 levels deep. Each spend publishes a one-way nullifier derived from the note's secret; spending within balance stays unlinkable, while reusing the same note produces a duplicate nullifier that exposes the double-spend attempt without revealing anything else. Anyone building zero-knowledge payment systems can track implementation details like this via daily.dev."}},{"@type":"Question","name":"What are the privacy limitations of zkAPI's anonymous API payment system?","acceptedAnswer":{"@type":"Answer","text":"zkAPI hides the payment link but not everything: a gateway can potentially correlate requests from a stable IP address, so users seeking stronger anonymity should route through Tor with a fresh circuit per session. On the content side, an inference provider can re-link sessions if prompts share personal details, writing style, or reused conversation history, since shared prompt contents act as fingerprints even when payment is anonymous. 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