Apple released iOS 7.1 on 10 March 2014, which includes support for CarPlay, fixes for Touch ID reliability and a bug fix for Home screen crashes.
YouTube channel iTwe4kz furnishes us with a great overview of the visual changes as well as what’s new with iOS 7.1:
iPhone 4 users are well represented in the iOS 7.1 update which addresses performance issues faced by iPhone 4 users since the introduction of iOS 7.
iOS 7.1 puts some speed back into iPhone 4 users experience albeit not quite at the same pace as iOS 6.1.3.