Whenever Apple launches a new gadget with a new screen size, iOS' current apps have to be made to fit them. Sometimes, the resolution of an app only needs to be doubled, as was the case with the iPhone 4 and Retina displays. For the iPhone 5's larger screen, developers had to do some work resizing their apps to make them taller. With the iPhone 6 (4.7 inches, 1334 x 750 pixels) and iPhone 6+ (5.5 inches, 1920 x 1080 pixels), Apple has cleverly kept the same 16:9 aspect ratio for its screen, which means current apps will automatically scale up to fit the device. "They just work," said Apple's Phil Schiller.
In scaling up, however, these apps won't retain the same pixel density — which means some apps might show some blurry edges and jaggies until developers scale up all their image assets. The text in many apps, however, may remain sharp if developers implemented Apple's default system text in their apps. Apps built for the iPhone 4 or 4S, which look mediocre on the iPhone 5 and 5S, will likely look even worse on the 6 and 6 Plus.
Additionally, given the size of the new iPhone screens, a new tweak in iOS will allow certain apps to run in an iPad-like landscape mode on the 5.5-inch iPhone 6 Plus. This mode, which is activated by turning the new device sideways, may show a new left-side column like on iPad if developers implement it. Other new software features for the largest iPhone include nice details like a pop-out email message (pictured above), a new 2-pane Stocks view (pictured below), and small touches like added photo avatars in the Messages app. In total, apps for the iPhone 6 Plus look a lot more like their iPad and iPad mini counterparts.