QuickPath Keyboard
Swipe-style keyboards are so common by now that it’s surprising Apple took this long to adopt the feature on its own keyboards. Sure, Apple offered the ability to add custom keyboards back in iOS 8, but not everybody wants to install a third-party keyboard, especially with the potential privacy implications involved.
Apple’s new QuickPath keyboard brings all of that swiping goodness to the built-in system keyboard, and it’s on by default so there’s nothing you need to do except just start using it. That said, if you really don’t want it to work that way, you can simply toggle off “Slide to Type” in the keyboard section of the main Settings app, and there’s also a “Delete Slide-to-Type by Word” setting here too that will let you choose whether you want to backspace over a whole word or only a single character for those times when your swipe gestures don’t quite come up with the right word.