One of the problems in previous Gears of War games was that all players had to have a specific map either unlocked or downloaded in order to play it with their friends in Horde Mode. This caused many matches to not happen between friends because of it.
However, at E3, Gears 4 director Rod Ferguson revealed that as long as the host players has the map in, all players will get it in Horde Mode. Thus eliminating the problem that plagued may a Gears of War gamer.
Gears of War 4 comes out October 16, 2016.