Following T-Mobile's heads up earlier today, Android 4.4.3 was just officially released by Google in the form of factory images and accompanying drivers. You can find builds KTU84M (Nexus 5) and KTU84L (Nexus 4, Nexus 7, Nexus 10) at the usual locations:
Those of you comfortable with flashing factory images, proceed to our guide. Otherwise, stay tuned for respective OTAs - the urls should be flowing in shortly.
As for the new stuff, we'll be combing through the changes we can touch shortly. In the meantime, feel free to reread the rumored human-readable, though probably incomplete, 4.4.3 changes or comb through the raw changelog that was prematurely posted a few weeks back.