As Adam Freeman wrote at APress.Pro Angular
Google has adopted an aggressive release schedule for Angular, starting with Angular 2.0. This means that there will be an ongoing stream of minor releases and a major release every six months. Minor releases should not break any existing features and should largely contain bug fixes. The major releases will contain substantial changes and may not offer backward compatibility. This schedule means that Angular 2.0 was released in September 2016 and will be followed by Angular 4.0 and Angular 5.0 in March and September 2017. (There will be no Angular 3.0 and Angular 2.0 will be followed directly by Angular 4.0). ref gbookpage - https://books.google.cz/books?id=WFQLDgAAQBAJ&pg=PA33&lpg=PA33
http://angularjs.blogspot.com/2017/03/angular-400-now-available.html
Jedi Angular Tips and Tricks
https://blog.dmbcllc.com/jedi-angular-2-tips-and-tricks/
origin - http://www.pipiscrew.com/2017/03/angular-v4-0-0-now-available/ angular-v4-0-0-now-available