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OpenAI-Compatible ChatGPT 5.5 Ultra and Codex API Docs

Last updated: July 12, 2026

Use the API key, base URL, and setup files delivered 10 minutes to 5 hours after payment.

Authenticate server-side, call ChatGPT 5.5 Ultra endpoints while 5.6 variants are paused, understand unlimited tokens with 4 concurrent connections, and prepare webhook receivers for billing or key lifecycle events.

Before code: Checkout, then manual setup (10 min-5 hr), then key by email + base URL. The snippets below work after delivery.

First request

const response = await fetch("https://unlimitedcodex.com/v1/chat/completions", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${process.env.UCX_API_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    model: "gpt-5.5",
    messages: [{ role: "user", content: "Write a release note for our AI feature." }]
  })
});