'Astral Codex Ten' is an anagram of 'Scott Alexander'. The blog is hosted on Substack, an online publishing platform. Although readers can opt for a paid subscription, Alexander notes that "[a]ll important ACX content is and always will be free." (Alexander 2021b)
Alexander, Scott (2021a) Still alive, Astral Codex Ten, January 21.
Alexander, Scott (2021b) What is Astral Codex Ten?, Astral Codex Ten.