After the initial panic and confusion around Google's decision to move to another new version of Angular so soon, we were quickly calmed by the clarification that it was actually Angular 2.x and not another huge rewrite as it was between 1.x and 2.
The article below gives us a brief overview of the new features in Angular 4.0
What's new in AngularJs 4.0? One of the most important things is that Angular 4.0 doesn't change that much. In Angular 4.0, some under the hood changes, some improvements, and performance improvements have been done. According to Angular change-log the "Angular 4.0 release is backwards compatible and will work with your existing code, but you may have use cases they haven’t anticipated"