Difference between AngularJS 1, Angular 2, 4 and 5
This happened because the libraries @angular/core, @angular/compiler and @angular/http had the version 2.3.0 and @angular/router already had version 3.3.0 and thus a common version jump should ensure that everything is consistent.
Angular 4 is not a big upgrade as it was then, but is more like Angular 2.4.0 with a new name to see. To avoid further confusion, the framework was renamed to Angular with no version name. For the most part, speed improvements have been made with Angular 5. Today, only AngularJS (version 1.x) and Angular (version 2+) are different.