GPTs vs Custom Instructions vs Project Instructions: which one should you use, and when?

If you've ever set up Custom Instructions, then built a GPT, then added Project Instructions and wondered "wait, which one of these is actually being used right now?", you're not alone. They overlap, they sometimes conflict, and most people end up using just one and ignoring the others.

Here's the simple frame I use:

Custom Instructions → tell ChatGPT who YOU are.

This is the stuff that's true in every chat: your business, your role, your voice, your defaults. Set it once, forget it, every conversation benefits.

GPTs → package up a specific JOB.

Build a GPT when you keep doing the same kind of task (generating LinkedIn posts, drafting cold emails, summarising calls) and you want a reusable tool with its own instructions, files, and behaviour. You can share GPTs with your team or the public.

Project Instructions → give ChatGPT context for ONE body of work.

Use Projects when you have a chunk of work with its own knowledge base, like a specific client, a course you're building, or a launch you're running. Inside that project, the instructions and files are scoped to it.

The order of override, in plain English:

In a normal chat → Custom Instructions apply.

Inside a Project → Project Instructions take priority over Custom Instructions.

Inside a GPT → the GPT's instructions take priority.

So: Custom Instructions for who you are. GPTs for what you do. Projects for what you're working on right now.

Pick the level that matches the lifespan of the task and you'll stop fighting yourself.

Cheers

Jason West 🙌

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