IOS 9

iOS 9 is the ninth major release of the iOS mobile operating system developed by Apple Inc., serving as the successor to iOS 8 and predecessor to iOS 10. It was announced on June 8th at the 2015 Worldwide Developers Conference, alongside tvOS 9, watchOS 2 and OS X El Capitan. Released on September 16, 2015, iOS 9 focuses less on new features and more on under-the-hood optimizations, as well as battery improvements. iOS 9 requires over 1 GB of free space to be downloaded onto supported iPhone or iPad models.

History
The first beta release of iOS 9.0 became available to registered developers right after the keynote event of the 2015 Worldwide Developers Conference on June 8, 2015. A public beta became available to members of Apple's Beta Software Program in July.

Currently the latest versions are iOS 9.3.5 for Wi-Fi only models, and 9.3.6 for cellular models to fix GPS issues.

iPhone

 * iPhone 4S
 * iPhone 5
 * iPhone 5C
 * iPhone 5S
 * iPhone 6
 * iPhone 6 Plus
 * iPhone 6S
 * iPhone 6S Plus

iPad

 * iPad 2
 * iPad (3rd generation)
 * iPad (4th generation)
 * iPad Air
 * iPad Air 2
 * iPad Pro (1st generation)

iPad Mini

 * iPad mini
 * IPad mini 2
 * iPad mini 3
 * iPad mini 4

iPod

 * iPod touch (5th generation)
 * iPod touch (6th generation)

Trivia

 * This is the last version of iOS to feature Slide To Unlock.
 * This is the last version of iOS to support devices that charge with 30-pin dock connectors.
 * This is the first version of iOS to use a new flat Music icon (the previous icon was originally going to be used).
 * This is the first version of iOS to feature a new flat switcher.
 * This is the first version of iOS to feature News, replacing Newsstand.