HOW CODEX IS BUILT

Summary from the TLDR Dev newsletter

OpenAI's coding agent, Codex, has a Rust-based architecture, open-source CLI, and "agent loop" that orchestrates user-model-tool interactions. Codex builds itself, generating over 90% of its own code, turning engineers into "agent managers" who oversee multiple parallel agents for tasks like feature implementation, code review, and bug fixing.