AngularJS was released in 2010 as a JavaScript framework for building client applications. As the core had to be further developed and the framework became too complex, the Angular team decided to rewrite the framework with TypeScript and thus in 2016 Angular 2 was released. After some minor upgrades, Angular 2.3 was switched to Angular 4 and Angular 3 was skipped.

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.