How to Use Codex: CLI Install, ChatGPT Sign-In, and Usage Limits

Codex is OpenAI’s coding agent: it can inspect a repo, edit code, run commands, and review changes. The four common surfaces are the CLI, the IDE extension, the ChatGPT desktop app, and Codex Cloud on the web. This guide walks through install, ChatGPT sign-in, your first task, and the December shared-usage change for Plus, Pro, and Business.

1. What Codex is, and where you use it

OpenAI describes Codex as a coding agent that inspects code, makes changes, and runs tools you already have, then waits for you to accept the result. Common entry points:

• Codex CLI: run codex in a terminal.
• IDE extension: VS Code, Cursor, Windsurf, plus Xcode and JetBrains integrations.
• ChatGPT desktop app: Codex mode with local permissions and browser features.
• Codex Cloud (web): tasks on OpenAI-managed machines that can continue while your computer sleeps; plan eligibility required.

Local clients support ChatGPT sign-in and API keys; Cloud requires ChatGPT sign-in.

2. Which plan, and who gets Cloud?

Help Center: Codex is included across ChatGPT plans, including Free and Go. Limits vary by plan—check your usage dashboard. The Codex pricing page characterizes personal tiers as:

• Free / Go: limited trial-style Codex access.
• Plus: a few focused coding sessions each week; Codex app and plugins.
• Pro: longer, higher-intensity sessions and higher Codex task capacity.

Codex Cloud is available to eligible Plus, all Pro tiers, Business, Enterprise, Healthcare, and Education (subject to rollout and workspace settings). It is not included with Free or Go. Guest, K–12, and Enterprise view-only seats cannot create cloud environments.

Shop reference prices checked 2026-11-06: Go ¥80, Plus ¥165, Pro 100 ¥800. USD list prices remain on openai.com/chatgpt/pricing. Plan picking details are in article 93.

3. Install the Codex CLI

Official standalone installer (macOS / Linux):

curl -fsSL https://chatgpt.com/codex/install.sh | sh

The same command updates Codex. Windows PowerShell:

powershell -ExecutionPolicy ByPass -c "irm https://chatgpt.com/codex/install.ps1 | iex"

Package managers:

npm install -g @openai/codex
brew install --cask codex

1. Install the CLI with one of the methods above, then confirm with codex --version or codex.
2. Open your project: cd into the repo root before starting.
3. First launch: run codex and pick a sign-in method.

In VS Code / Cursor / Windsurf, install the Codex extension and open the Codex sidebar (Command Palette: “Codex: Open Codex Sidebar” if the icon is missing).

4. Sign in with ChatGPT (recommended)

Default path is Sign in with ChatGPT. Complete the browser flow; credentials return to the local client. You can also run:

codex login

1. Start login: run codex or codex login and choose ChatGPT.
2. Authorize in the browser with your ChatGPT account.
3. Return to the terminal: CLI and IDE share the same cached login.
4. Headless / remote: if the localhost callback fails, use device code auth (enable it in ChatGPT security settings): codex login --device-auth.

Credentials may live in ~/.codex/auth.json or your OS keyring. Treat them like a password. Check with codex login status; clear with codex logout.

5. Alternative: API key sign-in

Useful for CI/CD or usage-based local work:

printenv OPENAI_API_KEY | codex login --with-api-key

Billing goes to the OpenAI Platform API account at API rates and does not use ChatGPT plan credits. Features that need ChatGPT workspace or cloud access are limited or unavailable; Cloud itself requires ChatGPT sign-in.

6. First task: prompts and usage

After sign-in, describe the goal in plain language. Create a Git checkpoint before large edits.

• /init: scaffold project AGENTS.md.
• /status: session config and remaining limits in an active CLI session.
• /permissions: when Codex may edit or run commands without asking.
• /model: switch model and reasoning effort; lower-cost models stretch limits.
• /review: review changes without modifying the working tree.

Also check the Codex usage dashboard or ChatGPT Settings → Usage. Auto-review safety checks are free when signed in with ChatGPT and do not count toward plan usage.

7. From December: shared ChatGPT and Codex usage

Help Center article “Understanding ChatGPT and Codex usage limits”: starting in December, Plus, Pro, and Business share a token-based allowance across ChatGPT and Codex as Work’s agentic features move into the main ChatGPT experience. Instant chat does not draw from that allowance. See remaining usage and reset times under Settings → Usage. When you hit the limit, wait for reset, upgrade, or buy credits. See also the update note on article 68.