As AI coding tools gain traction among software developers, their application now extends across all stages of the software development process, even enhancing the tools themselves. OpenAI has exemplified this trend, as revealed in recent interviews with Ars Technica.
OpenAI employees shared that Codex, their AI coding agent, is extensively used to refine its own capabilities. Alexander Embiricos, product lead for Codex at OpenAI, stated, “I think the vast majority of Codex is built by Codex, so it’s almost entirely just being used to improve itself.”
Introduced in May 2025 as a research preview, Codex functions as a cloud-based software engineering agent capable of performing tasks such as writing features, resolving bugs, and suggesting pull requests. The tool operates within secure sandboxed environments linked to a user’s code repository and can execute multiple tasks simultaneously. Users can access Codex via the ChatGPT web interface, a command-line interface (CLI), and IDE extensions for VS Code, Cursor, and Windsurf.
The name “Codex” traces its roots to a 2021 OpenAI model based on GPT-3, instrumental in GitHub Copilot’s tab completion feature. The name is believed to be a shorthand for “code execution,” tying the current iteration of Codex to its pioneering predecessor.
Embiricos highlighted the impact of the earlier model, saying, “For many people, that model powering GitHub Copilot was the first ‘wow’ moment for AI. It showed people the potential of what it can mean when AI is able to understand your context and what you’re trying to do and accelerate you in doing that.”
Displayed in ChatGPT, Codex’s interface bears some resemblance to Anthropic’s Claude Code, which debuted in February 2025. When questioned about Claude Code’s influence on Codex, Embiricos sidestepped a direct answer yet acknowledged the competitive spirit in the market. “It’s a fun market to work in because there’s lots of great ideas being thrown around,” he remarked, noting that OpenAI had developed Codex's features internally before releasing the CLI version, which came after the launch of Anthropic’s tool.