T-Mobile Samsung Galaxy S4 and Tab 3 receive unexpected security updates
It looks like the updates bring the February Android security patch (recently pushed to newer Android devices) to both the Galaxy S4 and Galaxy Tab 3. These are the first software updates that this phone and this tablet are getting on T-Mobile since 2015. However, the two devices still run the ageing Android 4.4.4 KitKat, and we're pretty sure this won't change (ever). Oddly, T-Mobile's Galaxy S4 seems to be the only version of the phone to be stuck on KitKat, since others variants have been updated to Android 5.0 Lollipop, but that's a different story.
Another relatively old Android phone that T-Mobile recently updated is the HTC Desire 626s, though this only received a December security patch.