# GPT55 x402 GPT API

GPT55 is an independent OpenAI-compatible x402 GPT API. It is not operated by OpenAI.

## Canonical buyer path

- Service hub: https://gpt55.558686.xyz/x402/service
- Machine catalog: https://gpt55.558686.xyz/x402/service.json
- Integration guide: https://gpt55.558686.xyz/x402/guides/ai-agent-x402-api
- Browser checkout: https://gpt55.558686.xyz/x402/service?checkout=standard-chat
- Browser wallet: sign from a buyer-owned wallet; no private key is sent to GPT55
- Standard route: POST https://gpt55.558686.xyz/v1/chat/completions/standard

## Current contract

- Model: GPT-5.6 Luna Standard
- Price: $0.00293 USDC per request
- Amount: 2930 atomic USDC units
- Network: Base, CAIP-2 eip155:8453
- Payment asset: canonical Base USDC
- Flow: quote-first request without payment -> HTTP 402 quote -> buyer-owned payment signature -> retry the same request -> HTTP 200 delivery

The live HTTP 402 response is authoritative immediately before payment. Never send a private key to the service. Quote requests, crawlers, health checks, and self-payments are not external revenue.

## Public source and quote-first client

- Source: https://github.com/wangletiand/gpt55-x402-gateway
- Quote-first client: https://github.com/wangletiand/gpt55-x402-gateway/blob/main/first-payment-client.mjs
- Lowest-friction canary: POST https://gpt55.558686.xyz/v1/tools/translate