"GitHub Copilot X is currently a representation of GitHub’s vision for the future rather than an available product offering of GitHub Copilot. As we continue to design, test, and build features that fall into the GitHub Copilot X vision, we are also taking the time to determine the best way to provide them to our customers."

From the FAQ at https://github.com/features/preview/copilot-x (When will GitHub Copilot X be available and how much does it cost?).