According to T-Mobile postings, Android 4.4.3 will be rolling out today for the Nexus 4, Nexus 5, and Nexus 7 (2013). All are listed as including "security enhancements" and "various bug fixes", but no new features, which isn't a surprise. The updates for the Nexus 4 and Nexus 7 are listed as build number KTU84L, while the Nexus 5 is listed as build KTU84M. The update is reportedly about 54MB which is about on par for an incremental update to a Nexus device.
Android 4.4.3 has also been rumored to be in internal testing for Samsung devices, and there was a soak test invite for T-Mobile Moto X users that could also be linked to the update. So, today may be the start of a number of devices getting the incremental fix. We'll keep you posted when we get more info on what exactly is in the update itself.