Hello,
guys from Bootstrap upgraded their framework a lot.
It looks really great. It uses SASS, flex and a lot of other cool features. If you still didn’t look at it, visit this guide http://bootstrap4.guide/
But its still in Alpha.
So, I want to ask you if you use BS4 on your templates.
I just switched from MaterilizeCSS to BSM4-b4 which is on top of BS4-b4…since its no longer in alpha there will not be any major breaking changes so its quite safe to start using it in production
I am thinking about moving to it also.
Looks great, but I will wait for a stable version 
Beta version means that its stable, more than alpha 
I would say, some kind of stable.
And how the @fredgrott said they will not make any major changes, so we can say its stable.