how to make UILabel autosize text in storyboard (or interface builder), NOT programmatically
On any element in Interface Builder you can select the element and hit...
Editor > Size to Fit Content (keyboard shortcut: CMD+=)
This will do a "sizeToFit" on the selected element. Labels will fit their text size, image view will resize to the image size, etc...
In Xcode 6.1, I had to set Content Compression Resistance Priority to a higher value, likely because I have other constraints that were conflicting, or causing the sizeToFit option to be disabled.
Before:
After:
