This is a bonus article for the “AI Path L1→L2 Upgrade Guide.” If you haven’t set up Codex yet, this guide gets you from zero to running.
On July 9, 2026, OpenAI made two announcements at once: GPT-5.6 went public, and Codex was merged into the ChatGPT desktop app. The new desktop app has three modes: Chat, Work, and Codex, all in one app. If you’ve already got the standalone Codex desktop app, it updates in place. Your projects and settings carry over.
Codex CLI was also updated on the same day to v0.144.0/v0.144.1, for terminal-first developers and CI/CD pipelines. Both paths work. Pick the one that fits your workflow.
This is the first hands-on article since Day 8, from account setup to running your first instruction.
GPT-5.6 Models and Pricing
The GPT-5.6 family has three models, each for a different use case:
| Model | Role | Input (per 1M tokens) | Output |
|---|---|---|---|
| Sol | Flagship reasoning | $5 | $30 |
| Terra | Daily balance | $2.50 | $15 |
| Luna | Cost-efficient | $1 | $6 |
Sol scored 80 on the Coding Agent Index, above Claude Fable 5’s 77.2. But not all plans give you access to every model: Free and Go users are limited to Terra. Plus and above can choose freely.
Both the Codex desktop app and CLI use credits from your ChatGPT plan. There’s no separate free tier for Codex. Here’s what each plan offers:
| Plan | Price | Codex Models | Notes |
|---|---|---|---|
| Free | $0 | Terra only, limited quota | Enough to try, not for heavy use |
| Go | $8/mo | Terra only, expanded quota | Light use on a budget |
| Plus | $20/mo | Sol/Terra/Luna, higher quota | Best for personal daily use |
| Pro | $200/mo | Same, higher quota, ultra available | Heavy daily use |
For most people, Plus is the better deal. The rest of this guide assumes you’re on Plus.
ChatGPT desktop app’s three modes: Chat, Work, and Codex — one app that switches between conversation, productivity, and development
Part 1: ChatGPT Plus Account
If you already have a ChatGPT Plus or higher subscription, skip to Part 2.
Create an Account
- Open a browser and go to chatgpt.com
- Click Sign Up with your email, Google, or Microsoft account
- Verify your email
- You’re now on the free tier
Upgrade to Plus
- Log in at chatgpt.com
- Click your avatar (bottom-left) → My Plan → Upgrade to Plus
- Select Plus ($20/month)
- Enter payment details
Payment Methods
On the web, OpenAI accepts major credit cards (Visa, Mastercard, American Express, Discover). PayPal is not supported for individual subscriptions. On mobile:
- iOS: Subscribe through the App Store, supports Apple Pay
- Android: Subscribe through Google Play, supports Google Pay
If your card is declined, common causes:
- Card issuer blocks cross-border payments: Call your bank to enable international transactions
- IP region is not supported: Make sure your IP is in a supported region
- Virtual cards: Some work, but some are rejected
Payment done, your account is upgraded. Codex credits are included.
Part 2: Install Codex — Desktop App (Recommended)
The ChatGPT desktop app is now a more straightforward way to use Codex.
Download and Install
Go to chatgpt.com/download and download the version for your system. If you’ve already got the standalone Codex desktop app, opening it triggers an automatic update. Your projects and settings carry over.
Switch to Codex Mode
Open the ChatGPT desktop app and switch to Codex mode at the top of the window. Desktop mode gives you:
- Local file system access — work directly on project directories
- Inline diff editing — every change shown as a diff
- PR review sidebar
- Multi-repo support
If you’re used to the old ChatGPT desktop, it’s now called ChatGPT Classic. You can switch between them freely. Codex mode can be set as your default view. On macOS, you can keep a standalone Codex icon in the dock.
Part 3: Or Use Codex CLI
If you prefer the terminal, OpenAI continues to maintain Codex CLI for terminal-first development, CI/CD, and scripting.
Prerequisites
- Node.js v18+ (v22 recommended)
- Git (Codex works best inside a Git repository)
Verify your Node.js version:
node --version
# Must return v18.x.x or higher
Install
npm install -g @openai/codex
macOS users can also use Homebrew:
brew install --cask codex
Verify
codex --version
A version number means it’s installed.
Link Your Account
Navigate to a project directory (a Git repo is best) and run:
cd /path/to/your/project
codex
On first launch, your browser opens for ChatGPT authentication. Once authorized, Codex starts its full-screen TUI.
The desktop app and CLI share the same credit pool. Authenticate once and you’re set. If you’re already logged into the desktop app, you don’t need extra authentication for the CLI.
Part 4: Your First Command
Both the desktop app and CLI let you type natural language instructions. Try this:
Explain this project's file structure and point out any problematic code
Codex reads your project files and gives you an analysis. Try something more specific:
Translate this README.md to Spanish, keep the Markdown format
Start with read-only instructions to get a feel for how Codex handles your project. Let it edit code once you’re comfortable.
FAQ
1. What’s the difference between Codex desktop and Codex CLI?
Desktop app is built into ChatGPT, with graphical diff review and a PR review sidebar. It’s a better fit for everyday coding. The CLI is a terminal tool, more for CI/CD and scripting. Under the hood they’re the same; desktop just adds a GUI. For auth, the desktop app uses your ChatGPT login, but the CLI needs a one-time OAuth flow.
2. Can Free users use Codex?
Yes, but with restrictions. You can switch to Codex mode in the ChatGPT desktop app with a Free account, but you’re limited to the Terra model with a reduced quota. Free accounts can’t use Codex CLI.
3. “Command not found: codex”
npm global binaries aren’t in your PATH. Add this to ~/.zshrc or ~/.bashrc:
export PATH="$PATH:$(npm prefix -g)/bin"
4. Authentication fails
For the desktop app, check that you’re logged into ChatGPT. For the CLI, verify your account is on Plus or higher.
5. Codex won’t edit files
By default, Codex runs in Suggest mode: it proposes changes but doesn’t apply them. Switch to Auto-Edit:
codex --approval-policy on-failure
In the desktop app, you can adjust the approval policy in Settings.
Setup Checklist
Desktop App
- ChatGPT Plus or Free account (logged in)
- Downloaded ChatGPT desktop app (chatgpt.com/download)
- Switched to Codex mode
- Sent first instruction to verify
CLI (Alternative)
- ChatGPT Plus or higher
- Node.js v18+ (
node --version) - Git installed (
git --version) - Codex CLI installed (
npm install -g @openai/codex) - Installation verified (
codex --version) - First run + OAuth authentication completed (
codex) - Sent first instruction to verify
This is a bonus article for the “AI Path L1→L2 Upgrade Guide.” Previous: Day 8: Autonomous Execution AI compared Codex, Claude Code, and OpenCode. If you prefer an open-source alternative, see OpenCode Cold Start.