OpenAI’s GPT-5 Codex: The AI That Builds Itself
▼ Summary
– OpenAI’s Codex, an AI coding agent, is now primarily used by the company to build and improve its own development tool.
– Launched in May 2025, Codex is a cloud-based agent that writes features, fixes bugs, and handles tasks in sandboxed environments linked to code repositories.
– The “Codex” name connects to a 2021 OpenAI model that powered GitHub Copilot, which was an early demonstration of AI’s potential to accelerate coding.
– OpenAI offers Codex through ChatGPT’s web interface, a command-line tool, and extensions for popular integrated development environments like VS Code.
– OpenAI acknowledges competition with tools like Anthropic’s Claude Code, noting a dynamic market where ideas are shared and development timelines overlap.
OpenAI’s advanced coding assistant, Codex, is now primarily responsible for its own development and enhancement, according to company insiders. This self-improving AI tool operates as a cloud-based software engineering agent, handling complex tasks such as writing new features, debugging code, and managing pull requests. It functions within secure, sandboxed environments connected to a user’s codebase and can process multiple jobs simultaneously. Available through ChatGPT’s web interface, a dedicated command-line tool, and popular IDE extensions, Codex represents a significant leap in autonomous AI development.
The product lead for Codex, Alexander Embiricos, recently explained that the system has reached a point where it builds and refines itself. “I believe the vast majority of Codex is built by Codex,” he stated, highlighting the tool’s recursive and self-sustaining nature. This modern version of Codex, released as a research preview, connects back to an earlier 2021 model that powered GitHub Copilot’s autocomplete feature. That initial model provided a pivotal moment for many developers, demonstrating how AI could grasp context and intent to dramatically accelerate workflow.
While the current command-line iteration shares some functional similarities with competing tools like Anthropic’s Claude Code, Embiricos emphasized the vibrant and innovative nature of the market. He acknowledged the competitive landscape but pointed out that OpenAI had been developing web-based features for Codex internally prior to the public CLI launch. The tool’s name, rumored internally to be shorthand for “code execution,” was chosen to honor that earlier foundational work, much of which was done by individuals who have since departed the company.
The evolution of Codex underscores a broader trend where AI systems are increasingly used to create and optimize their own frameworks. By operating in isolated environments linked directly to repositories, it can safely execute code and propose changes, streamlining the development process. This capability not only improves efficiency but also continuously elevates the tool’s own sophistication, creating a powerful feedback loop of advancement.
(Source: Ars Technica)
