The most important are:
On iOS 7 applications define a key color that indicates interactivity and selection state for UI elements throughout the app. So you obtain a great level of consistency over your app.
See Key Color to see how to use this feature in GeneXus.
iOS 7 introduces Dynamic Type, basically when you adopt Dynamic Type you get:
automatic adjustments to letter spacing and line height for every font size.
the ability to specify text style semantically such as Body, Footnote, etc
Text that responds appropriately when user change their prefferred text size settings.
See Dynamic Type to se how to use dynamic types in GeneXus.
All Screen Content
iOS 7 use full-screen layout , this means that the app content in a screen use the full-screen even if you have an Application Bar visible. This detail implies that if you are programming by hand you should change your programming to consider some extra pixels in the screen and more, you
should consider to change the color of the status bar depending on the content. For example if you have a dark content in your screen you should consider to have a light status bar and viceversa.
With GeneXus you don't need to worry about this underline change, GeneXus is going to do the hard work for you.
Icons & Launch Image
iOS 7 introduces new requeriments for Icons & launch images.
See iOS 7 Icons and Launch Images to see how to set them in GeneXus.
Rendering Mode in Images
iOS 7 allows to use the same image as a full image or just as a mask.
Rendering Mode property
All iOS 7 controls have an updated appearance, and most of them also have different metrics.
Programming by hand implies this tat that if you were relying on some fixed metrics you could have problems when converting to iOS 7. This is not a problem for GeneXus users, since this type of compatibility issues is resolved automatically by GeneXus.
iOS 7 introduces interactive transitions that GeneXus automatically uses for their transitions. Basically are transitions where you can see the entering content and the old content.
There are many apis that were introduced with iOS 7 that GeneXus is using now internally hiding the complexity of using one for iOS 6 and other for iOS 7. For example Location APIs are using a new api that saves battery life.
All these changes are done under the hood when targeting iOS 7.