What is OpenAI Codex?
Codex is the coding agent from OpenAI, the company behind ChatGPT. It reads a project's codebase, edits files, runs commands and tests, and proposes changes for you to approve. It works with your ChatGPT account: in the ChatGPT desktop app for macOS, Windows and Linux, in the terminal, inside your code editor, in the browser and in the iPhone app.
Unlike an editor with built-in AI, Codex works like a teammate you hand a whole task to. It can work on your computer, on local files, or in OpenAI's cloud, where long tasks keep running even when your computer is off. It is included in ChatGPT subscriptions, so anyone already paying for Plus can start at no extra cost.
Main Features
- Whole-project work: reads the codebase, edits multiple files and runs tests and commands
- Cloud tasks: long jobs run in remote environments, started and followed from web, desktop or phone
- Many surfaces: ChatGPT desktop app, terminal (Codex CLI), extension for VS Code, Cursor and Windsurf, built-in integration in Xcode and JetBrains
- Code review: automatically reviews pull requests on GitHub
- Integrations: connects to Slack and other tools through plugins
- Model and speed choice: different GPT-6 models and a Fast mode for quicker answers
How Does OpenAI Codex Work?
Install the ChatGPT desktop app, sign in, pick Codex from the menu and open your project folder. Then describe what you need, for example fixing a bug or adding a feature: Codex explores the files, applies the changes and shows a diff you can accept or discard. If you prefer the terminal, Codex CLI installs with a single command on macOS, Linux and Windows.
For longer tasks you choose to work in the Cloud: Codex sets up an environment connected to your repository, does the work remotely and returns a result to review. You can start a task on your computer and check on it from your phone.
Who is OpenAI Codex for?
- Developers who already have a ChatGPT subscription
- Teams that want automatic pull request reviews
- Freelancers working on several projects at once
- Anyone who wants to delegate long tasks to the cloud
- Companies using ChatGPT Business or Enterprise
Use Cases
- Fixing bugs starting from an error message
- Adding a feature that touches several files in a project
- Writing tests and fixing the ones that fail
- Reviewing pull requests before merging
- Understanding and documenting an unfamiliar codebase
Pricing
Codex is included in every ChatGPT plan. On Free and Go ($8/month) access is limited: only the GPT-6 Luna model in the desktop app, and the feature is still rolling out. Full use starts with Plus at $20/month: Codex on web, terminal, editor and iPhone, code review, Slack integration and the GPT-6.1 Sol and GPT-6 Luna models.
For heavy use there is Pro in three tiers: $100, $200 and $500 per month. Pro plans currently have no five-hour limit like Plus. When you run out of usage you can buy extra credits. Alternatively, Codex works with an API key on pay-as-you-go pricing, but without the cloud features.
Pros and Cons
Pros:
- Included in ChatGPT, no extra cost for Plus subscribers
- Works on desktop, terminal, editor, web and phone
- Cloud tasks keep running even with your computer off
Cons:
- Very limited access on the Free and Go plans
- On Plus, the five-hour limits run out quickly on big tasks
- It edits files and runs commands: always review the changes
Final Verdict
OpenAI Codex is one of the most complete coding agents available today, with the advantage of already being part of ChatGPT. For Plus subscribers it is the easiest option to try; developers who code for many hours a day should consider Pro. If you want an agent outside OpenAI, compare it with Claude Code and GitHub Copilot.