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What Is OpenAI Codex? The Coding Agent Explained

Codex is OpenAI's coding agent: a desktop app, a command-line tool, IDE extensions and cloud tasks that read your code, make changes and run commands. What it does, how it differs from the old 2021 Codex model, what it costs with ChatGPT plans, and how it compares with Claude Code.

Codex is OpenAI's AI coding agent. You describe a task — fix this bug, add this feature, write tests for this module — and Codex reads your code, makes the changes, runs commands to check them, and shows you the result.

Not the Codex from 2021

The name has been used twice, which causes confusion. In 2021, "Codex" was an OpenAI model that powered the first version of GitHub Copilot. That model was retired.

Today's Codex is a product: an agent that runs on OpenAI's current models. If an old tutorial talks about calling the "Codex API", it's about the retired model, not this.

The ways to use it

Codex comes in several forms that share your account:

  • Codex app — a desktop app for running and supervising agent tasks.
  • Codex CLI — an open-source agent that runs in your terminal, working on the files on your computer.
  • IDE extension — Codex inside VS Code and similar editors.
  • Cloud tasks — hand off a task and Codex works on it in a cloud sandbox connected to your GitHub repository, then proposes a pull request.

What Codex does well

  • Delegated tasks. Give it a well-defined job and let it work, especially in the cloud while you do something else.
  • Running several tasks in parallel in separate sandboxes.
  • Fitting into GitHub — reviewing pull requests, proposing changes as PRs.

It reads an AGENTS.md file in your project for instructions, the same file several other tools use. (AGENTS.md vs CLAUDE.md)

How much does it cost?

Codex is included with ChatGPT plans. As of October 2026, per OpenAI's pricing: the free plan includes the Codex desktop app only; Go ($8/month) adds the CLI and IDE extension; Plus ($20/month) and above add cloud tasks; Pro starts at $100/month. You can also use an OpenAI API key and pay per use. Check OpenAI's pricing page for current limits.

Codex vs Claude Code

They're close competitors with a similar shape: terminal agent, IDE integration, desktop app, cloud tasks.

Codex Claude Code
Company OpenAI Anthropic
Models OpenAI's GPT models Claude models
Cheapest way in Free (app only) or Go at $8/month Pro at $20/month
CLI open source Yes No
Instructions file AGENTS.md CLAUDE.md (also reads AGENTS.md)

For a full comparison, see Claude Code vs Codex.

Things to know before you start

  • Use Git. An agent can change many files quickly; commit before each task so you can undo. (Git for beginners)
  • Give it a way to check its work — tests, a build command — and ask it to run them.
  • Review what it changed before merging. (How to review an AI-written PR)
  • It writes code; it doesn't host it. Your app still needs to be deployed somewhere.

The summary

  • Codex is OpenAI's coding agent, not the retired 2021 model.
  • Available as a desktop app, CLI, IDE extension and cloud tasks.
  • Included with ChatGPT plans; the CLI is open source.

EasySpawn gives the app your agent builds a permanent home: a server with your code, database and HTTPS — and a terminal where any agent can keep working on it. See how it works or join the waitlist.

Related: Claude Code vs OpenAI Codex · What Is an AI Coding Agent? · Best AI Coding Tools in 2026 · OpenAI API vs Claude API

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