iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
Apple Begins Offering 'Last Compatible' Version of Apps for Users Running Legacy Versions of iOS
The move comes as Apple is set to release iOS 7 tomorrow, with the new operating system featuring a complete redesign along with a number of new features including an overhaul of multitasking, a new universal settings window known as Control Center, and changes to the Notification Center. With all of the changes coming in iOS 7, some developers are redesigning their apps to be compatible with only iOS 7, and Apple's new system offers one way for users who have yet to upgrade to iOS 7 to continue using apps while also providing reminders that they are not running the most current version of iOS.
iOS 7 will be avaliable for free and will be compatible with the iPhone 4, iPhone 4S, iPhone 5, fifth-generation iPod touch, iPad 2, iPad with Retina Display (third- and fourth-generation), and the iPad mini, along with Apple’s new iPhone 5c and iPhone 5s.