Codex founding engineer explains why Rust, why open source, and how the harness works
mathemagie · x · 2026-09-10
Gergely Orosz of The Pragmatic Engineer sat down with Thibault Sottiaux, who started building Codex, for a 100%-Codex deep dive. Topics include his time at Google and why he joined OpenAI, the early days of Codex, why it's built in Rust, why it's open source, how it plays nice with other models, how the harness works plus harness-vs-model improvements, the SDLC and code review practices behind Codex, maintenance and architecture, how AI tools expand what engineers can do, the ChatGPT + Codex merge, and advice for engineers who want to work in AI.
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