Abstract

The web learned how to ask for money before it learned how to ask who you are. HTTP received its payment status code (402 Payment Required) in 1997; it never received an identity one. x402 revived 402 to let servers charge autonomous agents for access. x401, introduced by Proof in June 2026, is the identity counterpart: a challenge-response protocol layered on HTTP 401 Unauthorized in which a server requires an agent to present a cryptographically verifiable proof of identity or authority, that a real, verified human (or a legitimately standing organization) authorized the action, before granting access.

This paper specifies how the Zetrix Agentic Wallet implements x401 as a native capability, reusing the same wallet service that already speaks x402. It maps the x401 challenge/presentation flow onto Zetrix's existing decentralized-identity stack (ZID Verifiable Credentials, BID-method DIDs, on-chain credential registries), defines the concrete message formats, and shows how x401 (authority) and x402 (payment) compose into a single full agentic transaction: prove who authorized you, then pay, then act. Version 1.0.0 reconciles the paper with the approved design and architecture.