Bootstrap 4 is a major rewrite of almost the entire project. The most notable changes are summarized immediately below, followed by more specific class and behavioral changes to relevant components. Browser support Dropped IE8 and iOS 6 support. v4 is now only IE9+ and iOS 7+. For sites needing either of those, use v3. Added official support for Android v5.0 Lollipop’s Browser and WebView. Earlier