Windows 10 build 18970 started rolling out to Fast ring Insiders yesterday. The build includes a new tablet experience for 2-in-1 PCs, the ability to reset your PC back to a fresh state through a cloud download, and brings the new Cortana experience to everyone.
The most notable change in this build is the new tablet experience. When a user flips a 2-in-1 PC around while running this build, the new experience automatically activates. It has spaced out touch targets along the taskbar, a File Explorer optimized for touch, and the touch keyboard automatically pops up when you tap within a text field.
The new tablet experience is separate from Windows 10 Tablet Mode, which is still present in this build and can be toggled on and off as usual.