TIER_B · protocol release

x402 HTTP transport specifies 402 headers, not body-only protocol

The x402 HTTP transport spec states that servers signal payment with HTTP 402 and a PAYMENT-REQUIRED header, clients send PAYMENT-SIGNATURE, and servers return PAYMENT-RESPONSE. Response bodies are an implementation concern; protocol information lives in headers.

Event 1 February 2026 · source 1 February 2026 · zFinia published 7 September 2026 · retrospective

Why it matters

Buyer-conformance bugs often come from stuffing metadata into the wrong layer. Header-valid 402 beats keyword-stuffed JSON.

Sources

https://github.com/x402-foundation/x402/blob/main/specs/transports-v2/http.md