Original Link: http://blog.getbootstrap.com/2015/08/19/bootstrap-4-alpha/
Major changes in Version 4. Some highlights:
- Moved to Sass from LESS
- Improved version of box-sizing as part of their new reset.
- Opt-in (single variable toggle) to use flexbox on the grids/components.
- Type set mostly in rems
And another big move for them: monitization through purchaseable themes designed by Bootstrap team themselves.