The first reports suggesting that Google is on the verge of releasing the Android 4.4.3 update for Nexus 4, Nexus 5, Nexus 7 2013, and other supported Nexus devices surfaced a few weeks ago, showing that we might be dealing with bug-fixing update rather than a major one. New sources quoted by Android Police claim that Google has started Android 4.4.3 KitKat dogfooding, meaning that the new firmware is has "entered internal testing outside of the core Android team."
Anyway the final release won't be made available for public right away, as most of us will have to wait a few more weeks.
The same source says that Android 4.4.2 aka KitKat MR2 (the Android 4.4.1 and Android 4.4.2 updates were labeled KitKat MR1) is now being made available for 1% of Google employees that are not a part of the Android team. For the time being, the dogfooding is only available for Nexus devices, but it's also expected to show up on Google Play Edition terminals, and Moto X.
If you're wondering what devices are set to receive the Android 4.4.3 update in the first wave, I remind you that the Nexus line-up (Nexus 4, Nexus 5, Nexus 7 2012, Nexus 7 2013, Nexus 10) is Google's main priority, followed by Google Play Edition devices (Samsung Galaxy S4 GPE, Sony Xperia Z Ultra, Moto G, LG G Pad 8.3, HTC One M7, and HTC One M8), and most likely Motorola's flagship for 2013, the Moto X, a handset that received KitKat updates very early.
At the moment, there's no knowledge of new features introduced by Android 4.4.3 KitKat, but the update is expected to bring a number of bux fixes for data connection, camera, Bluetooth, random reboots, USB debugging, WiFi, MMS, Email/Exchange, Calendar, People/Dialer/Contacts, DSP, IPv6, VPN, and many more.
Even though the folks at Android Police gave the Android 4.4.3 rumor a confidence rating of 9/10, we are advising you to take it with a pinch of salt as nothing is official until Google says so. The bottom line, however, is that you shouldn't expect the Android 4.4.3 OTA update to hit your device just yet.