OpenAI has launched a research preview of Codex, its most advanced AI coding agent. Codex enhances AI-driven software engineering and is available to subscribers of ChatGPT Pro, Team, and Enterprise, with plans to expand access to Plus and Edu users. This technology is powered by Codex-1, a fine-tuned reasoning model based on O3.
According to OpenAI’s announcement, it delivers cleaner code, precise instruction-following, and autonomous testing and debugging.
Unlike earlier models, Codex operates as a cloud-based agent in a secure, sandboxed environment, integrating with GitHub to engage with users’ codebases. It autonomously handles tasks like feature development, bug fixes, code queries, and pull request generation, running for 1–30 minutes based on complexity. Users assign tasks via ChatGPT’s “Code” option, track progress transparently, and query specific files, as detailed by OpenAI.
00:00 Introducing Codex
01:38 Setup and kicking off tasks
05:05 Environments
07:20 Guiding Codex with a Markdown file
12:00 The Codex origin story
14:25 Verifying and reviewing Codex tasks
17:28 Using Codex at OpenAI
20:48 Availability via ChatGPT
21:22 Roadmap and Codex CLI… pic.twitter.com/fqNvGwW8UQ
— OpenAI Developers (@OpenAIDevs) May 16, 2025Codex is entering the booming AI developer tools market, competing directly with established players like Anthropic’s Claude Code and Google’s Gemini Code Assist, as well as fast-growing startups such as Cursor ($300M revenue) and Windsurf. TechCrunch reports that OpenAI may acquire Windsurf for $3 billion, though the deal remains unconfirmed. Agents Research Lead Josh Tobin called Codex a “virtual coworker,” aiming for ChatGPT to handle days-long engineering tasks, per a product briefing.
Codex refuses malicious code requests and operates in an air-gapped environment, minimising misuse risks. OpenAI’s Codex CLI, using the o4-mini model, is available via the API at $1.50/$6 per million input/output tokens. A Microsoft study cited by OpenAI notes debugging challenges, underscoring ongoing AI limitations.
Part of ChatGPT’s evolution into a multi-functional platform with agents like Sora and Operator, Codex positions OpenAI as a leader in AI coding.
