According the official website of bootstrap (http://www.getbootstrap.com), version 4 is about to be released soonest. Meanwhile, an alpha version (4.0.0-alpha.6) has been released prior to the official release of version 4 which we are all anticipating.
This alpha version comes with exciting features. Check components/features of the new release via this link. https://www.v4-alpha.getbootstrap.com/component/