ChatGPT used to be one thing: a chat box. Now it has three modes, and once you know what each one is for, choosing is easy.
Chat, Work and Codex are places to work. Chat runs on GPT-6, with a Thinking slider that sets how hard it thinks. Work and Codex have their own model choices (GPT-6 Astra, GPT-6.1 Sol, GPT-6 Sol and GPT-6 Luna, depending on your plan). Choose the workspace for the job, then choose its model.
Here is the whole guide in one line: Chat is for answers. Work is for finished projects. Codex is for building software. If you remember nothing else, remember that.
At A Glance
Chat is your assistant. Quick answers, ideas, drafts, learning. Available anywhere.
Work is your operator. Finished files: spreadsheets, decks, reports, websites. Best on desktop.
Codex is your engineer. Building apps, tools and code. Choose a local project on desktop or a Codex Cloud environment that you can reach across devices.
Where You Can Use Them
Free and Go get limited Work on the desktop app only. Paid plans (Plus, Pro and Business) include Work on desktop, web and mobile. Codex is built into the ChatGPT desktop app on every plan, including Free, with bigger limits on paid plans. Codex Cloud runs coding tasks from desktop, web or mobile where available. Organization settings and your plan control access and usage. Local projects still need their own computer.
Chat: Your Everyday Assistant
This is the ChatGPT you already know and probably already use. It is fast, conversational and free. You ask, it answers. The basics have not changed, and for a huge chunk of what people do with AI, this is still the right tool.
Use Chat when you want to ask a quick question, bounce around ideas, get a fast answer, write something short, or learn a new topic. If what you want is an answer or a quick bit of text, Chat is your mode. It is the one you reach for a dozen times a day.
Examples of good Chat asks
Explain compound interest like I'm 12.
Give me 10 name ideas for a coffee brand.
Reword this email to sound friendlier: [paste email]
What's a good weeknight dinner with chicken and rice?
Where to find it
It is the normal ChatGPT. In the desktop app, Chat is the default side of the Chat / Work switch, and on web or mobile it is just the standard chat you already open. Nothing to switch on.
Work: Your Operator
This is the big one. Work replaced the old agent mode, and instead of answering in the chat, it takes on a whole project and hands you finished work. You give it an outcome and it goes and does it, for as long as the job takes.
Hand Work a big task and it breaks the project into steps, pulls from your connected apps and files, and works in the background, sometimes for hours, until it hands you the finished thing: a real spreadsheet, a full slide deck, a written report, even a working website. Not a draft in a chat box you have to copy out. An actual file.
The one sentence that explains Work
Chat gives you answers. Work gives you deliverables. If you would normally take ChatGPT's answer and then go do the actual work yourself, Work is the mode that does that part too.
Examples of good Work tasks
Take the files in this folder and build me a spreadsheet with totals by category, then a 5-slide summary of the key numbers.
Research these 5 competitors and build me a one-page comparison of their pricing and positioning.
Where to find it
In the desktop app, flip the Chat / Work switch at the top to Work. On web, click the Work tab. On mobile, switch from Chat to Work at the top of the screen. Same account, just a different mode. For a full walkthrough, see my ChatGPT Work guide.
Tip: Work shines when you point it at real material, a folder of files, your connected apps, or specific links, and tell it exactly what finished thing you want. The clearer the brief, the better the deliverable.
Codex: Your Engineer
Codex is the mode for when you actually want to build software. An app, a tool, a website, or fixing something inside an existing codebase when it breaks. And here is the part that matters for most people: you do it by talking in plain English. You do not need to have written a single line of code in your life.
Use Codex when you want to build an app or a tool, spin up a working website, or fix and change existing code. If the end result is a piece of working software, Codex is your mode. (If you just want a simple hosted website, ChatGPT Sites may be even easier.) For everything that is not code, Work or Chat will serve you better.
Examples of good Codex asks
Build me a simple website where people can sign up for my newsletter.
Something in my app broke and it won't load. Find the problem and fix it.
Where to find it
In the desktop app, use the ChatGPT / Codex switcher to open Codex for local projects. For Codex Cloud, select an available cloud environment and describe the task. You can continue cloud tasks from web, mobile or desktop without keeping your computer awake. The cloud environment needs its own repository, tools and access.
Do not let the word engineer scare you. You talk to Codex the same way you talk to Chat, in normal words. It handles the actual code. If you have ever thought "I wish I could just build a little tool for this", this is the mode that makes that possible without a course.
Can I Continue on My Phone?
Yes, eligible new synced Work tasks can continue across desktop, web and mobile. Enable sync before creating the task. Older tasks keep the mode they started with.
If a step needs files or apps on your computer, keep that computer online and connected. Cloud work can continue independently with the files and connections available in its environment. For coding, Codex Cloud provides its own environment and supports continuing across devices.
Which One Do I Use?
When you are not sure, run down this list.
Get a quick answer or explanation: Chat
Brainstorm, or draft something short and fast: Chat
Learn about a new topic: Chat
Turn a big project into a finished file: Work
Build a spreadsheet, deck or report from your data: Work
Have it pull from your apps and work for hours: Work
Build an app, tool or website: Codex
Fix or change something in code: Codex
The tell, if you are still stuck
Ask yourself what you want back. Want an answer, words on a screen? That is Chat. Want a thing, a finished file you would otherwise build yourself? That is Work. Want software, something that runs? That is Codex.
The One-Page Cheat Sheet
Chat. It is your assistant. Best for answers, ideas, drafts and learning. You get back a reply in the chat. Available on every plan and device. One word: answers.
Work. It is your operator. Best for finished projects and files. You get back a real file: a sheet, deck, report or site. Flip the Chat / Work switch to Work. One word: deliverables.
Codex. It is your engineer. Best for building software. You get back working code or an app. Use the ChatGPT / Codex switcher in the desktop app, or Codex Cloud across devices. One word: software.
Your Action Plan
- Open the ChatGPT desktop app so you have all three.
- Keep using Chat for quick stuff, nothing changes there.
- Next time you would normally spend an hour building something, switch to Work and hand it the whole task.
- If you have got a little tool or site in mind, try Codex and just describe it.
That is the whole thing. Chat for answers, Work for finished projects, Codex for building software. Now you are in the 1% who actually knows when to use each.
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