x401 vs. x402 at a glance

Dimension	x402	x401
HTTP status	402 Payment Required	401 Unauthorized
Question asked	Can you pay?	Who authorized this, and are they allowed?
Server → agent	PAYMENT-REQUIRED	PROOF-REQUEST / PROOF-REQUIRED
Agent → server	PAYMENT-SIGNATURE	PROOF-RESPONSE / PROOF-PRESENTATION
Proof object	Signed payment authorization / on-chain transfer	Verifiable Presentation (VP) of one or more VCs
Verified against	Facilitator (/verify, /settle)	Issuer public keys (deterministic, offline)
Zetrix primitive	ZETRIX / JMYR (ZTP20) transfer, Facilitator settlement	ZID VC + BID DID + on-chain issuer/revocation registry
Reusable session	Payment channel / receipt	OAuth 2.0 token-exchange → short-lived Bearer token

The two are orthogonal and composable. A high-value action typically requires both: authority (x401) then payment (x402).