How can I downgrade my iPhone to iOS 9?

iPhone 6s

iPhone owners looking to downgrade from iOS 10 to the previous version (iOS 9.3.5) are out of luck. This week, Apple stopped signing the latest iOS 9 firmware. This means that downgrading to the earlier operating system is not possible. At this time, the only versions of iOS that can be installed are iOS 10.0.2 and 10.0.3. Apple released iOS 10.0.3 exclusively for the iPhone 7 and iPhone 7 Plus. For all other iPhones iOS 10.0.2 remains the current version.

UPDATE: Apple released iOS 10.1 on October 24, 2016.

Apple has stopped signing iOS 10.0.1 in addition to iOS 9.3.5. When it comes to jailbreaking, the inability to downgrade to iOS 9.3.5 is irrelevant, since this version of iOS could not be jailbroken anyway. Pangu Team may working behind the scenes to jailbreak iOS 10, however there is no timetable for a release. The most recent version of iOS that can be jailbroken is iOS 9.3.3.

In just over a month, reports have indicated iOS 10 is already installed in over 70 percent of compatible Apple mobile devices. iOS 10 can be installed on the iPhone 5 or later. The latest iOS includes many new features and changes to the interface, such as removal of the long-standing "slide to unlock" screen. Apple is expected to release iOS 10.1 in the next week or two.

One of the main highlights of iOS 10.1 will be portrait mode for the iPhone 7 Plus. This feature combines imagery from the standard and telephoto lenses to simulate a shallow depth of field. This brings DSLR-quality photography one step closer to reality for mobile devices.