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OpenAI Codex
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freemium Code Assistants

OpenAI Codex

OpenAI Codex is an AI coding agent that works through ChatGPT to complete software tasks asynchronously. It writes code, runs tests, and creates pull requests in parallel, achieving 85–90% success on well-defined tasks. Available on web, iOS, GitHub, and

OpenAI Codex is a cloud-based software engineering agent that works through ChatGPT, allowing developers to delegate coding tasks asynchronously without constant supervision. Unlike the original 2021 Codex autocomplete model, the current version is powered by codex-1, a software-engineering-focused variant of OpenAI’s o3 model. Released in research preview in May 2025 and later expanded to ChatGPT Plus users, it has grown to around 4 million weekly active users. Codex’s biggest advantage is parallel task execution. Developers can assign multiple coding jobs simultaneously, letting the agent write code, run tests, and generate pull requests while they focus on other work. Users report that 30–40% of their daily coding output is generated by Codex, with an 85–90% success rate on clearly defined maintenance tasks such as API development, bug fixes, CRUD operations, and authentication updates. The platform works through ChatGPT, GitHub, iOS, and the open-source Codex CLI. However, it performs best with well-scoped requirements and struggles with ambiguous architectural decisions. Users cannot choose the underlying model, and its 56.8% SWE-Bench Pro score shows limitations on complex professional tasks. Full cloud-agent access also requires a paid ChatGPT subscription.