The ChatGPT app includes three tools that look almost the same when you open it: Chat, Work, and Codex. It also lets you pick a model (Sol, Terra, or Luna). The catch is that they don't all cost the same to run. Pick the wrong one for a simple task and you can use up your credits in an afternoon without realizing it.
These tools run on shared, expensive AI capacity that everyone at CES draws from. Using the right one for each task is how we keep access open to everyone.
The one rule to remember
For almost everything you do, use Chat.
- Use Work only when you need a finished, multi-step document or project.
- Ignore Codex unless you write code.
Remember that much and you'll rarely go wrong. The rest of this article explains why it matters.
The three tools
| Tool |
Use it for |
What it costs you |
| Chat |
Everyday questions, search, brainstorming, quick tasks, and summarizing |
Light. Chat runs on its own separate, lower usage. |
| Work |
Longer, multi-step deliverables: documents, spreadsheets, presentations, reports, research and analysis, and Sites |
Heavy. Draws from the shared credit pool, so use it deliberately. |
| Codex |
Software development only: writing and debugging code, running tests and commands, and working with code repositories |
Heavy. Draws from the same shared pool as Work. Desktop app only. |
Work and Codex share the same credits and usage limits. They pull from the same heavier pool, while Chat runs on its own lighter usage. So moving from Chat into Work or Codex is a bigger jump than it looks.
A costly mistake to avoid
Say you want to summarize an email.
If you open Codex to do it, you'll probably find it already set to Sol. Paste in the email, ask for a summary, and it works. But you've just used the heaviest tool (Codex) and the most expensive model (Sol) for a task that needed neither. Do that a few times and your credit budget can be gone in a couple of hours, with no obvious reason why.
The better move is to stay in Chat. Summarizing is exactly what Chat is for. It's fast, it runs on the lighter usage, and you can do it all day without watching your credits.
This is an easy mistake, and it's not really your fault. The app shows you all three tools at once, and Codex opens on Sol by default. That default is meant for software engineers doing heavy coding work, not for everyday tasks. For most of what BYU-Idaho employees do, it's the wrong place to start.
Which model should you pick?
Inside any of these tools, you also choose a model. The short version:
- Terra is the right default for most people.
- Switch to Luna when you want to stretch your credits or run a lot of similar tasks.
- Save Sol for genuinely hard problems. It's the most capable model, and it burns credits the fastest.
- If a model lets you set a reasoning effort, start low. Higher effort costs more credits, so raise it only when a task really needs it.
For the full details on credits, usage, and choosing a model, see CES OpenAI Frequently Asked Questions.
When you're not sure, use the web or mobile app
There's a simple safeguard built in. On the web and in the mobile app, your only choices are Chat and Work. Codex shows up only in the desktop app.
So when you're not sure, use ChatGPT in a browser or on your phone. You can't open the most expensive tool by accident.
Quick decision guide
- Quick question, search, summary, brainstorm, or short draft? Use Chat.
- A multi-step document, spreadsheet, report, presentation, or Site? Use Work.
- Writing or debugging real code? Use Codex, in the desktop app.
- Not sure? Open ChatGPT on the web or your phone, where you'll only see Chat and Work.
- Which model? Start with Terra, drop to Luna to save credits, and keep Sol for the hard stuff.