Just got my AT&T unlocked G850A in Israel, with Kitkat on board.
Tried to update OTA, tried to update with Kies, but no go.
Current firmware is g850aucu1anl1.
My advice would be to stick with Kitkat. Lollipop has made my Alpha very unresponsive when bringing up task manager. Also simple tasks like launching the dialer is much slower. After pressing a button you have to wait 2-3 seconds before any indication it is doing something.