Ethereum Foundation introduces zkAPI for private, unlinkable API payments

The Ethereum Foundation announced zkAPI on October 1, describing an implementation for private usage credits across metered APIs. The project allows users to deposit credits into an Ethereum vault and prove authorization for a bounded amount of service use without tying an identity to every request.

zkAPI is aimed at AI inference and other services that charge by usage. Rather than relying solely on conventional API keys associated with an account, the system uses zero-knowledge proofs to validate that a user has sufficient credit and is permitted to consume a defined amount of service.

The Ethereum Foundation said zkAPI is running on Ethereum mainnet and was built with the Open Anonymity Project. The underlying usage-credit design was previously published on Ethereum Research in February by Davide Crapis and Vitalik Buterin.

How zkAPI changes API payment authorization

The model separates the act of funding service usage from the authorization presented to a provider. A user deposits credits into an Ethereum vault, then generates a zero-knowledge proof that supports a limited API request or set of requests.

This approach is intended to avoid making an identity-linked API key the central payment credential for every call. The proof establishes authorization for metered use while limiting the information disclosed through the payment mechanism.

The design is a privacy layer for payment authorization, not a replacement for the API service itself. Providers can still meter their services, while users can draw against credits held in the vault.

• Users deposit usage credits into an Ethereum vault.
• Zero-knowledge proofs authorize bounded service consumption.
• The system is designed for AI inference and other metered APIs.

Runtime-key mode separates request traffic from settlement

The implementation includes a runtime-key mode for AI-related requests. In this arrangement, the client obtains a short-lived key with a spending cap, then sends prompts directly to the AI provider.

The payment server is responsible for proof verification and settlement. This division is intended to separate payment information from the provider’s request traffic, rather than routing prompts through the payment system.

The announcement places the work within Ethereum’s broader cryptographic and privacy-oriented development agenda. Related discussion has included Ethereum’s longer-term cryptographic world computer vision for 2030.

• The client receives a short-lived, capped runtime key.
• Prompts are sent directly from the client to the AI provider.
• The payment server verifies proofs and handles settlement.

Privacy limits remain part of the design

The Ethereum Foundation explicitly noted that zkAPI does not itself provide network anonymity. Network-level information may still be relevant outside the proof and payment authorization process.

The system also does not guarantee that a prompt cannot identify a user or be correlated with other activity. In practice, the privacy properties described by zkAPI apply to the linkage between usage-credit payments and API authorization, not to every possible source of identifying information.

That distinction is important for evaluating the implementation. Zero-knowledge proofs can reduce data exposed in a particular authorization flow, but they do not eliminate privacy risks created by request contents or network metadata.

• zkAPI does not provide network anonymity by itself.
• Prompt content may still identify or correlate a user.
• The stated privacy benefit concerns payment and authorization linkage.

Continue reading: Ethereum’s cryptographic world computer vision for 2030 on BTCNews.

Continue reading: Ethereum schedules Glamsterdam activation on Sepolia on BTCNews.

Sources

• Ethereum Foundation Blog: Introducing zkAPI: private usage credits for any API
• Ethereum Research: ZK API Usage Credits: LLMs and Beyond
• The Open Anonymity Project: Unlinkable Inference as a User Privacy Architecture

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