Yes. See Apple's iOS8 documentation specifically, size classes:
iOS 8 makes dealing with screen size and orientation much more versatile. It is easier than ever to create a single interface for your app that works well on both iPad and iPhone, adjusting to orientation changes and different screen sizes as needed. Design apps with a common interface and then customize them for different size classes. Adapt your user interface to the strengths of each form factor. You no longer need to create a specific iPad storyboard; instead target the appropriate size classes and tune your interface for the best experience.
There are two types of size classes in iOS 8: regular and compact. A regular size class denotes either a large amount of screen space, such as on an iPad, or a commonly adopted paradigm that provides the illusion of a large amount of screen space, such as scrolling on an iPhone. Every device is defined by a size class, both vertically and horizontally.
There is also a very good tutorial video on the WWDC site.
In order to stop your iPhone 6/6+ app being scaled, add a launch image of the correct size or better, use a launch storyboard.
From there you should use AutoLayout and avoid hard coding to screen sizes. In the long run it'll be a lot less effort and less error prone.