OpenAI Codex describes two AI-assisted software development tools released by OpenAI. They translate natural language into code, a technology described by artificial intelligence researchers as an AI agent.
On August 10, 2021, OpenAI announced Codex, a code autocompletion tool available in select IDEs such as Visual Studio Code and Neovim. It was a modified, production version of GPT-3, finetuned on gigabytes of source code in a dozen programming languages. It was the original model powering GitHub Copilot.
On May 16, 2025, OpenAI announced the launch of a research preview of a distinct tool with a similar purpose, also named Codex, based on a finetuned version of OpenAI o3. It is a software agent that performs tasks in computer programming, including writing features, answering codebase questions, running tests, and proposing PRs for review. It has two versions, one running in a virtual machine in the cloud, and one where the agent runs in the cloud, but performs actions on a local machine connected via API (similar in operation to Cursor or Claude Code). It is available to ChatGPT Pro, Enterprise, Team, and Plus users.
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