Ionic v3 project in Ionic v4

I have a project made with Ionic 3 (now I have ionic v 3.20).

If I upgrade Ionic to Ionic 4, my project will compile?

Thanks in advance.

Ionic CLI is not Ionic Framework.
If you upgrade your Ionic CLI from 3.20.0 to 4.x, your project itself will still be Ionic Framework 4 and work as before.