x402 Protocol Skill

Facts current as of July 2026 — verify pricing and model IDs against https://docs.claude.com, and protocol/package details against the x402 docs.

Protocol Overview

x402 embeds stablecoin payments into HTTP by using the 402 "Payment Required" status code. A server responds with payment requirements; the client signs a payment authorization, resubmits the request, and gets the resource after verification and settlement.

Payment flow:

1. Client sends HTTP request → Server returns 402 + PAYMENT-REQUIRED header (base64 JSON)
2. Client reads requirements, creates signed payment payload
3. Client resubmits request with PAYMENT-SIGNATURE header (base64 JSON)
4. Server verifies payment via facilitator POST /verify
5. Server performs work, settles via facilitator POST /settle
6. Server returns 200 + resource + PAYMENT-RESPONSE header (contains txHash)