Android 4.4 KitKat might have rolled out to quite a few Samsung devices already, but the update is yet to start making its way to most of the low-end and mid-range phones in the company's lineup. We've heard that Samsung has been working on those updates and is also planning on bringing Android 4.4.3 to some of its devices, and thanks to our insider, we've obtained info on where the company stands regarding said updates. Starting off with Android 4.4.3 (build number KTU70), the yet-to-be announced version of Android is currently being tested on the Galaxy S5 (both the Exynos and Snapdragon models) and the LTE-A variant of the Galaxy S4 (GT-I9506A).
However, Android 4.4.3 is only being integrated with Samsung's own software and features at the moment, so it will likely not be made available for a month or so (Google will probably roll it out by the end of this month or sometime in June before Google I/O, after which we can expect to see it rolling out to the Galaxy S5 and other devices.) It's also a bit strange that 4.4.3 is currently being integrated into the Galaxy S4 LTE-A – from what we know, Android 4.4.2 is actually being tested on that device, but since it hasn't rolled out yet, we might see the handset skipping directly to 4.4.3 in the future.
As far as older, more modestly powered phones are concerned, it seems that Samsung is on track to follow the time frame that we've seen in the past. Devices like the Galaxy Grand 2, Galaxy Mega 5.8, and the Galaxy Mega 6.3 are undergoing final testing and should get the Android 4.4.2 update sometime in June. Like the Galaxy S4 LTE-A, some of these devices might skip directly to Android 4.4.3 as well, so it's possible that the update's rollout could be pushed into July or later.