The firmware update goes by the build name KTU8AF (KTU8 was the previously speculated Android 4.4.3 build number for the Nexus 5), and enables the device to work on Sprint's LTE network on bands 26 and 41. The network operator on support page mentions that the update will be available starting 14 April and will be rolled out completely to other users in stages.
With Android 4.4.3, Google has reportedly fixed problems with data connection loss, random reboots, missed calls and various camera bugs. Other than existing bug fixing, the Android 4.4.3 is said to not bring anything new in terms of features and UI interface.
So far, the update has not been listed on Google's factory Images for Nexus Devices page, but it is speculated that it will soon be available to other users in U.S, as the 'KTU' text code is usually used for all the Nexus 5 unlocked U.S variants.
Earlier a report citing sources suggested that Android 4.4.3 is undergoing the dogfooding stage, and Google has given it to 1 percent of its employees. It is apparently limited to the Nexus line of devices - namely the Nexus 4, Nexus 5, Nexus 7 2012, Nexus 7 2013 and Nexus 10. The report further noted that the update is also expected to soon roll-out to Google Play Edition devices from HTC, Samsung, LG, Sony and Motorola.From the dogfooding stage to the release, the Android 4.4.3 update seems to have travelled quickly and can be expected to roll-out the same way to other users.