OpenAI launches Codex, a coding assistant integrated into ChatGPT

OpenAI today announced the launch of Codex, an AI coding agent integrated directly into ChatGPT. This new tool aims to transform software development by enabling users to delegate a wide range of coding tasks, from writing new features and fixing bugs to answering codebase questions and proposing pull requests.

According to OpenAI's official announcement, Codex is powered by Codex-1, a specialized version of their o3 model fine-tuned for software engineering tasks. This AI agent has been trained using reinforcement learning on real-world coding scenarios, allowing it to generate code that closely mirrors human style, adheres to instructions precisely, and can even iteratively test its own work until it achieves a passing result.

How Codex works

Codex operates within isolated, cloud-based sandbox environments, each preloaded with the user's repository. Accessible through a dedicated sidebar in ChatGPT, users can assign tasks by simply typing a prompt and clicking "Code," or ask codebase-related questions by clicking "Ask."

Codex can read and edit files, as well as execute commands like test harnesses, linters, and type checkers. Task completion times are reported to range from 1 to 30 minutes, depending on complexity, with users able to monitor progress in real-time.

A key feature highlighted in the announcement is the ability to guide Codex using AGENTS.md files within a repository. These text files allow developers to provide instructions to Codex on how to navigate the codebase and how to adhere to project-specific best practices.

Preventing malicious use

OpenAI has taken measures to prevent the misuse of Codex for malicious purposes, such as malware development. The model has been trained to identify and refuse requests aimed at such activities while still supporting legitimate and beneficial coding tasks.

Early success stories

Early adopters from companies like Cisco, Temporal, Superhuman, and Kodiak have been testing Codex, reporting significant potential in accelerating feature development, debugging issues, writing tests, refactoring codebases, and even enabling non-engineers to contribute lightweight code changes.

In addition to the ChatGPT integration, OpenAI also announced updates to Codex CLI, a lightweight open-source coding agent that runs in the terminal. A smaller, faster version of codex-1, specifically designed for the CLI and API, is now available as "codex-mini-latest." OpenAI has also simplified the process of connecting developer accounts to Codex CLI.

Availability and pricing

Codex is initially rolling out to ChatGPT Pro, Enterprise, and Team users globally, with support for Plus and Edu users expected soon. The company has said it will be offering generous access at no additional cost for an initial period. This will then be followed by rate-limited access and flexible pricing options. The "codex-mini-latest" model for API users is priced at $1.50 per 1M input tokens and $6 per 1M output tokens, with a prompt caching discount.