The Galaxy S4 was released on the 1 April 2013^[1], which marks the beginning of its update period. On the 2 October 2015, the Android 6 was released, a next version of the operating system, which not made available for the Galaxy S4, thus leaving Galaxy S4 on the the previous version of the operating system, the Android 5^[2]. This date marks the end of what we consider its update lifetime.

These two dates are 2 full years and 6 full months apart, which gives it F tier.