Twitter characterizes the redesign as making it easier to “navigate between all of your tabs.” Replacing the top tabs that previously merged with the app bar, navigation is now more reachable for users with larger devices. The FAB for New Tweet or Message remains in the bottom-right corner though is now slightly higher.
However, this bottom bar comes at the expense of being able to swipe between Home, Search, Notifications, and Messages. Additionally, the navigation bar is no longer solid black. That bar is either a grayish white or a dark blue depending if Night mode is disabled/enabled.
The action bar that notes what part of the app you’re in and what account you are logged into disappears when scrolling, while Notifications gains two new tabs for All and Mentions that can be swiped between. In direct messages, the Message request count is at the top of the screen.
This server-side update is beginning to roll out as of Thursday afternoon. Try closing Twitter from the Recents menu and reloading the app if it’s not yet available for you.