A lot of class names/functions have changed. Some are completely gone and replaced by others.

But the good news is: Form now on there won't be changes in class names/functions anymore. There will be only extensions when a new version (4.x) comes out.

Beta 2 released 19 Oct 2017....still looks like a Beta 3 next and then a final Beta 4 before the final release. No update on Bootstrap Builder...still Alpha

Bootstrap 4 Beta 3 released December 29th "The Final Countdown".