Google released new update of Android, Android 4.4.3 Kitkat . And it is available for all Nexus devices (4,5,7 lineups). Other Smartphone manufacturers will also provide upgrade to their current versions, but it will take one or two months.
Motorola begun the upgrade process for Moto X, Moto Gn and Moto E. Also OTA firmware available for HTC devices.
This new update is to fix some errors and improvements. This upgrade will not change UI completely but will give some new things.