ChatGPT Codex: What It Is and How to Use It (2026)
ChatGPT Codex is an autonomous coding agent built into ChatGPT. It can write features, fix bugs, review pull requests, and run tests inside isolated cloud environments — all without you staying at your keyboard. Available to Plus, Pro, Business, Enterprise, and Edu users as of July 2026.
What Is ChatGPT Codex?
ChatGPT Codex is OpenAI's autonomous coding agent. Unlike asking ChatGPT to write a snippet in a regular chat, Codex works on complete software engineering tasks from start to finish. It reads your codebase, edits files, runs tests, and commits changes — all inside a secure, isolated cloud environment.
Codex launched as a standalone app in May 2025 and merged into the main ChatGPT desktop app on 9 July 2026 — the same day OpenAI introduced ChatGPT Work. Today, more than 5 million people use Codex every week, and over 1 million of them use it for work outside software development.
How Codex Differs From Regular ChatGPT Coding Help
When you ask ChatGPT to write code in a normal conversation, it generates a snippet and hands it back to you. You copy it, paste it, test it yourself, and fix any issues. Codex works very differently.
With Codex, you assign a task — for example, "Fix the login timeout bug" or "Add unit tests for the payment module" — and Codex works on it inside a sandboxed environment loaded with your actual repository. It reads your files, runs your test suite, iterates until tests pass, and commits the changes. Tasks typically take between 1 and 30 minutes depending on complexity.
The key difference: Codex completes the task asynchronously. You can close your laptop, and it keeps working. When it is finished, you review the result, open a pull request, or ask for further changes.
How to Access ChatGPT Codex
Codex is available directly inside the ChatGPT desktop app and on the web. There is no separate app to install — as of July 2026 it is built into ChatGPT itself.
Here is how to get started:
Download the ChatGPT desktop app (Mac or Windows) and sign in with a Plus, Pro, Business, Enterprise, or Edu account.
Select the Codex tab from the top navigation bar.
Connect your GitHub (or GitLab) account to give Codex access to your repositories.
Type your task in plain English and press Code to start. Use Ask if you want Codex to answer a question about the codebase instead.
Codex runs in the background. Check back when it notifies you, review the changes, and open a pull request or request revisions.
What Tasks Codex Handles Well
Codex performs best on tasks that are well-scoped and verifiable. The more clearly you define what done looks like — for example, "all existing tests pass and no new lint errors" — the better the results.
Tasks that work well with Codex include:
Writing new features based on a specification or ticket description.
Fixing bugs, including ones that are difficult to reproduce manually.
Writing and expanding unit tests and integration tests.
Large-scale refactors, such as renaming variables or migrating a function to a new pattern across many files.
Writing and improving documentation.
Reviewing pull requests and surfacing potential issues before merging.
Security scans of GitHub repositories for vulnerabilities (via Codex Security Cloud).
Codex Cloud: Running Tasks When Your Laptop Is Off
Codex Cloud, launched at DevDay 2026 in September, takes the asynchronous nature of Codex further. Tasks run in reusable cloud environments with your repository, tools, and dependencies pre-loaded. Each task gets its own isolated workspace.
This means you can start a task from your phone, review progress from any device, and the work keeps running even when your computer is asleep. For teams, Codex Cloud provides shared environment settings so everyone works from the same configuration.
Which ChatGPT Plans Include Codex?
Codex is included at no extra cost across the following ChatGPT plans:
Plus ($20/month) — included usage for focused coding sessions each week.
Pro (from $100/month) — higher usage limits to support full workdays across multiple projects.
Business — secure shared workspaces with admin controls and flexible team pricing.
Enterprise and Edu — full admin governance, including spend controls and workspace permissions.
The Codex CLI is free to use with an OpenAI developer account. It runs in your terminal and supports local, real-time coding assistance. The cloud-based agent (described above) requires a paid ChatGPT plan.
How to Guide Codex With an AGENTS.md File
One of the most useful features in Codex is the AGENTS.md file. Like a README but written for the agent, you place an AGENTS.md file in your repository to tell Codex how to navigate the codebase, which commands to run for testing, and what coding conventions to follow.
A simple AGENTS.md might include: the test command to run before committing, the file structure for new features, naming conventions for variables and functions, and any linting rules the project uses. With this context, Codex performs significantly better on your specific codebase than it would without it.
Frequently Asked Questions About ChatGPT Codex
Is ChatGPT Codex free?
The Codex CLI (command-line interface) is free to use with an OpenAI developer account. The cloud-based Codex agent inside ChatGPT is included with Plus, Pro, Business, Enterprise, and Edu plans. There is no free plan access to the cloud agent at present.
What programming languages does Codex support?
Codex supports all major programming languages including Python, JavaScript, TypeScript, Go, Rust, Java, C++, Ruby, and more. It works across any language your repository uses, and its performance is strongest on languages with large training datasets such as Python and JavaScript.
How does Codex access my code? Is it safe?
Codex connects to your GitHub or GitLab repository via authorised OAuth. Each task runs in an isolated, sandboxed cloud environment. Codex cannot access external services or APIs during task execution unless you specifically configure it to. All changes are committed for your review before they are merged.
What is the difference between Codex and GitHub Copilot?
GitHub Copilot works in your code editor, suggesting code as you type in real time. Codex is an autonomous agent that takes on complete tasks independently in the background. They are complementary: Copilot helps while you are actively writing code, while Codex handles tasks you assign and works on them without your ongoing involvement.
Can Codex review pull requests automatically?
Yes. Code Review in Codex, launched at DevDay 2026, lets Codex automatically review pull requests, summarise changes, surface potential issues, and answer questions about specific sections. It can also run automatic reviews on new pull requests in the cloud so a first pass is ready before a human reviewer opens the PR.
What model does ChatGPT Codex use?
As of October 2026, ChatGPT Codex uses GPT-6.1 Sol as its default model for most tasks. GPT-6 Astra is available for higher-complexity work on Pro 500 and Enterprise plans, including the Ultrafast speed tier. The Codex CLI uses a lightweight model (codex-mini-latest) optimised for low-latency terminal use.
The Bottom Line
ChatGPT Codex is the most significant step forward in AI-assisted software development since autocomplete suggestions. It does not just help you write code — it does the work independently and hands you the result to review.
Whether you are a solo developer looking to move faster, or part of a team wanting to automate repetitive engineering tasks, Codex is worth exploring. Start with one well-scoped task and see how the result compares to doing it yourself.
