Proof, the identity-verification company, launched x401 earlier this year as an open, issuer-neutral protocol for verifying the human behind an AI agent's actions, and it's now pushing that proposal into formal standards territory. The company says it will submit x401 to the FIDO Alliance's agentic authentication standards workgroup, moving the protocol from a vendor release toward a body that already sets passkey and authentication specs used across the web. The design is narrower than it sounds. x401 doesn't try to verify the AI agent itself — it verifies who authorized it. The protocol extends HTTP 401-style challenges: instead of a username-and-password prompt, a service can ask an agent to present a cryptographically signed Verifiable Credential covering a specific claim — identity, age, organizational affiliation, signing authority — before letting the agent proceed. The service checks the issuer, the claim, the scope, and the action, then decides whether to let the transaction through. That separation of identity from authorization is deliberate, and it's also where x401 tries to avoid becoming a single point of lock-in. Any conforming issuer can deliver credentials, any agent can present them, and each service sets its own bar for which issuers and assurance levels it trusts. Circle, an early backer, frames the split cleanly: x402 handles how an agent pays, and x401 handles who it is. Proof's own reference implementation runs on OID4VC issuance and presentation, letting a person verify to an IAL2 assurance level and reauthenticate later with a biometric rather than re-proving identity from scratch each time. The FIDO submission matters because the agentic-identity space right now is a pile of competing vendor specs — Proof's x401 is one of several, alongside things like ERC-8004 and LOKA, each proposing its own answer to 'who's actually behind this agent action.' Getting a workgroup seat at FIDO doesn't guarantee x401 becomes the standard, but it does put the proposal in front of the same body that already shepherded WebAuthn and passkeys into near-universal browser support. Eight live demos — opening a bank account, filling a prescription, and others — are already running end-to-end, which is further along than most competing proposals in this space have gotten. Whether this becomes infrastructure or stays a well-marketed vendor spec depends on whether other issuers actually show up. Proof says it's recruiting AI platforms and relying parties to join, and the real test is whether services outside Proof's own customer base start issuing or accepting x401 credentials on their own terms.