The Extreme Windows blog states that one change in Windows 8.1 will offer a new option to increase the percentage of text and other items on a display up to 200 percent, or "Extra Large." This compares to the "Larger" upper limit in Windows 8 where you could only go up 150 percent on text and items.

There are a lot of things apps can do to optimize the user experience for DPI scaling. If we take a photo editing app as an example, there are some very important considerations. A photo editing app may want to scale UI elements like buttons and checkboxes, but not scale other content. If we consider the image viewing area of the app it may be critically important that that portion of the UI not be scaled. If the image viewing area of the app was automatically scaled to 200% you'd never be able to see your photo at native resolution because it would be pixel doubled. This could be a problem if the reason you bought that 4K display was to see more of your images at native resolution!

Windows 8.1 provides APIs for apps to know what the optimal scaling value is. If you were developing that photo editing app, you could scale the toolbars and chrome based on the optimal scaling value and leave the image viewing area at 100% scale. Perfect!

One example of an app that responds to DPI scaling in the Windows 8.1 Preview is IE 11. IE 11 uses the API to determine the optimal zoom level and adjusts it automatically.