There doesn't seem to be any rhyme or reason to which carriers release updates for their Android updates first, and once you stray outside of the shallow waters of flagship smartphones, things start to get really inconsistent. For example, AT&T is updating its carrier-specific version of the Samsung Galaxy Tab 4 8.0 to 5.1.1 today, at least according to this support page. But at the same time, Sprint's Galaxy Tab 4 7.0 is only just now getting upgraded from Android 4.4 to 5.0. Huh.
AT&T's Tab 4 8.0 update includes changes to the Quick Settings menu, but not much else on top of the usual changes updates. The OTA file is huge, over 800MB, so you might as well follow AT&T's insistence that you only update on a Wi-Fi network. Oddly, while Verizon's version of the Galaxy Tab 4 8.0 was upgraded at the same time as its Galaxy Note Pro 12.2 (which probably means that the company got the firmware from Samsung at the same time), there's no mention of AT&T's Note Pro 12.2 being updated at the moment. We'll keep a look out.
Sprint's cheaper Note 4 7.0 has only been updated once before now, way back in January to add the Kid's Mode application. The latest update won't actually go out until September 26th according to the support page, but when it does it will be the only notable software bump in over a year. On top of 5.0 you get a Stagefright patch. Sprint doesn't say how big the Android 5.0 upgrade will be, but expect it to be pretty sizeable, and make room on your tablet accordingly.