Smith, who tested Codex for a month and ended up rewriting a bunch of his apps and shipping versions for Windows and Android: I spent one month battle-testing Codex 5.3, the latest model from OpenAI, ...
OpenAI’s GPT‑5.4 mini is now available in the API, Codex, and ChatGPT, whereas GPT‑5.4 nano is only available in the API.