How to figure out what the Android Software Update is?
I tried a few methods I could think of:


Wireshark the WiFi packets -> nothing
adb logcat to see if anything extra info is logged -> nothing
I found out thought, that most of what we see on the "Update" screen is hard-coded and only the "Improved stability..." part is dynamic.
adb pull /cache/fota/update.zip or adb pull /data/fota/update.zip -> requires root


After almost giving up I found http://sammobile.com. The sad thing is that it only works for Samsung phones, which I have luckily. The fact that my phone's origin is German or Austrian and the date the update showed up helped me narrow it down to
12-11-2014 Firmware Updates:

Germany (DBT)                   GT-I9505    GALAXY S4 LTE   4.4.2   I9505XXUGNK4
Germany (Black Edition)(DBT)    GT-I9505    GALAXY S4 LTE   4.4.2   I9505XXUGNG8


and since I already have I9505XXUGNG8, it must be the first one, which is weird because I would swear the color is black like this

Then I checked the carrier's listing: 
http://www.sammobile.com/firmwares/database/GT-I9505/DBT/ which seems to correspond with the timings of my past received the updates. So I checked my CSC (*#1234#) and found that indeed this is my current version so the update is still 4.4.2.

Edit

I did the update and after checking About device it was indeed updated to I9505XXUGNK4.