It's all programmatically. It looks like Adobe Dreamweaver WYSIWYG editor from 20 years ago is now in Xcode. Apply UI in the canvas and it instantly generates code for you, though how much you can control is a ?, how well it does what you want remains to be seen.
This is kind of concerning to me, as it seems to make controlling the layout precisely difficult. One of the great advantages of xibs is that the UI you layout in IB is just data, not code. You can use multiple xibs with different UIs that share the same controller (when it makes sense). Bringing this "web" style of development to native apps is not very appealing to me. But I'll give it a shot, at some point.