OpenAI's ChatGPT desktop app hides a full office suite inside it. Simon Willison found the app, formerly known as Codex, caches a 1.7GB runtime in ~/.cache/codex-runtimes/codex-primary-runtime, complete with its own Python and Node.js installations, git, the Poppler PDF library, and a headless build of LibreOffice, the open source office suite that forked from OpenOffice.org in 2010.
The bundled tools are not dead weight. A documents plugin inside the runtime includes skills that tell Codex how to find and use those binaries, which reveals how OpenAI gives its coding agents local document power. With LibreOffice running headless, the agent can convert and edit Word, Excel and PowerPoint files without calling a cloud service, while Poppler handles PDF rendering and extraction.
Bundling native runtimes is a deliberate tradeoff: first-run downloads get heavier, but the agent gains reliable, offline-capable tools with predictable versions. Willison notes the app has since rebranded to ChatGPT, and the cache folder exposes the engineering underneath. For founders building AI agents, it is a useful reminder that shipping your own runtime stack, rather than assuming a clean machine, is often what makes an agent actually work in production.