Building Codex with Tibo Sottiaux
Summary
Codex was built in Rust a year before ChatGPT launched, proving the language's viability for AI agents—but the real lesson is that maintenance becomes a scaling tax that automation will eventually eliminate, fundamentally changing how code review works inside AI-forward teams.
Key Takeaways
- Rust was chosen for Codex despite the model not being available for distribution in Rust at the time, because the team recognized early that Rust would be 'quite good for agents' with focused effort—a strategic bet on language fit over existing ecosystem convenience.
- New team members are immediately told 'Have you asked Codex?' as the first response to questions, indicating AI-first development culture where the code generation tool is the primary reference system, not documentation or senior engineers.
- Maintenance is reframed as 'a tax that you pay over time to keep things running,' but this tax is being automated away—shifting the burden from engineers to AI systems, which fundamentally changes operational costs and team structure.
- Code review's role is actively changing within OpenAI teams; it's no longer about catching bugs but about something else entirely—implying AI-generated code requires different validation frameworks than human-written code.
- Codex was merged into ChatGPT rather than remaining standalone, suggesting that specialized AI coding tools consolidate into general-purpose models—a consolidation pattern relevant for founders building AI products.
Related topics
Transcript Excerpt
A fun story that you recently shared on X as well is how you were part of the team that built this internal Google bot that was Chad GPT but a year before Chad GPT >> that caught up like you know wildfires. It felt more than a research [music] project >> for Codeex you built it in Rust and at the time the model was not on distribution for Rust. >> Turns out it was quite clear that Rust as a language would actually be quite good for agents fairly quickly if we decided to put some effort into it. When someone joins the Codeex team, what do you tell them? How do things get done here? >> The thing that they hear the most about when they have a question is like, "Have you asked Codex?" It still surprises new starters that you can basically ask it anything. >> Building was the fun part, but then…