Taking up the extra space on the side of the keyboard are designated cut, copy, and paste controls, with the rest of the keyboard's buttons gaining a smaller width to accommodate the one-handed mode. Discovered to be dormant since iOS 8, without an official beta or public launch, the feature's original code ties into the launch of Apple's size-bumped 4.7-inch iPhone 6 and 5.5-inch iPhone 6 Plus.
Today's fun hack (been there since at least iOS 8); the iOS keyboard has an unused left/right one-handed mode. Activated by edge-swipe pic.twitter.com/zIk7x7CVmu— Steve T-S (@stroughtonsmith) October 19, 2016
Troughton-Smith noted in a few tweets that the keyboard could potentially be hacked on an actual iPhone like he did with the iOS Simulator, but the device would need to be jailbroken to do so. The developer gave some context regarding the code of such a jailbreak tweak, as well as a video of the one-handed keyboard in action.
Reachability is an answer to vertical problems when using the Plus-sized iPhones with one hand, but it leaves horizontal, one-handed typing issues unsolved in iOS keyboards. Apple could debut the one-handed keyboard in a future version of iOS, potentially next year's iOS 11, but since the code for the feature has remained dormant for so long already, it's impossible to tell.