OpenAI Codex Review: The Agent vs. The CLI (2026 Guide)

OpenAI has a naming problem.

If you hear "Codex," you might think of the 2021 model that powered GitHub Copilot. That's ancient history.

The new Codex (2026) is actually two different tools sharing the same brain:

1. Codex Agent: A cloud-based engineer that lives in ChatGPT Plus ($20/mo) or Pro ($200/mo).
2. Codex CLI: A free terminal tool that lives on your laptop.

Both use the new codex-1 (o3) reasoning models. Both claim to be "autonomous." But they are for completely different types of developers.

I spent the last week building apps with both. Here’s the breakdown.

The Codex Agent: The "Hands-Off" Engineer

This is the one getting all the hype on X. If you subscribe to ChatGPT Pro, you get access to "Codex" mode.

It’s not just a chatbot anymore. It’s a full environment. When you ask it to "build a snake game," it doesn't just spit out code blocks—it spins up a cloud sandbox, writes the files, runs the server, and gives you a preview URL.

The "O3" Difference

The secret sauce here is the reasoning model. Unlike GPT-4o, which rushes to give you an answer, codex-1 (built on o3) takes a breath. It "thinks" for about 10-30 seconds before writing a single line of code.

It plans the architecture. It checks for edge cases. It realizes that react-scripts is deprecated and switches to Vite without you asking.

The good:

• Zero setup: You don't need Node, Python, or Docker installed. It’s all in the browser.
• Project awareness: It remembers the whole file structure it created.
• GitHub Sync: It can push the final result directly to a new repo.

The bad:

• It’s a walled garden. You can't easily edit the files it creates with your own VS Code setup unless you sync via GitHub.
• Latency. Waiting 45 seconds for a "thinking" pause just to change a button color is painful.

The Codex CLI: The "Vibe Coder" Tool

This is the tool for the rest of us. The ones who live in the terminal.

The Codex CLI (@openai/codex) is basically OpenAI's answer to Aider. You install it with npm install -g @openai/codex, run codex, and suddenly you have a senior engineer inside your terminal.

How it works

It reads your local files. It sees your git diffs. When you say "refactor this to use Tailwind," it modifies your actual files on your actual disk.

The "vibe" here is immaculate. You don't have to copy-paste code blocks. You don't have to alt-tab to a browser. You just stay in your flow.

The killer features:

• Auto-Edit Mode: If you trust it, you can let it modify files without confirming every chunk. It’s terrifyingly fast.
• Screenshot-to-Code: I pasted a screenshot of a dashboard into the terminal (yes, the terminal), and it adjusted my CSS to match.
• Price: It’s free if you bring your own API key. And since you can use gpt-4o for cheaper tasks, it’s remarkably affordable.

Head-to-Head: Agent vs. CLI

Feature	Codex Agent (Cloud)	Codex CLI (Local)
Where it lives	ChatGPT Browser Tab	Your Terminal
Best model	codex-1 (o3)	gpt-4o / o3 (API)
Setup	None (Instant)	npm install
File Editing	Cloud Sandbox Only	Local Filesystem
Cost	$20/mo (Plus)	Pay-per-token
Vibe Score	85 (High friction)	98 (Pure flow)

Comparison: Codex vs. The World

For a deeper dive, check out our full comparisons of Codex Agent vs. Devin and Codex CLI vs. Aider. But here is the summary:

Codex Agent vs. Devin

Devin is still the king of long-running tasks. If you need an agent to "go away for 3 hours and migrate my database," Devin is better. Codex Agent times out after about 30 minutes of autonomy. But for quick, interactive prototyping? Codex is faster and feels more "conversational."

Codex CLI vs. Aider

Aider is the open-source champion. It supports Claude 3.5 Sonnet (which many devs still prefer over o3). It has better git integration.

However, Codex CLI has a cleaner UI. It feels more like a product and less like a hacker tool. If you are 100% into the OpenAI ecosystem, Codex CLI is seamless. If you want to use Anthropic or local models, stick with Aider.

Looking for more options? Read our guide on the Top 5 Alternatives to OpenAI Codex.

Verdict: Which one should you use?

Use the Codex Agent if:

• You are a Product Manager or Founder prototyping ideas.
• You don't want to mess with local environments.
• You already pay for ChatGPT Pro.

Use the Codex CLI if:

• You are a Developer with an existing codebase.
• You hate copy-pasting code.
• You prefer pay-per-token pricing over a subscription.

Personally? I cancelled my Pro subscription and stuck with the CLI. The ability to vibe code in my own terminal, with my own keybindings, using my own local files... that's the future.