State of Decay 2 is getting a new DLC pack called Daybreak on September 12. The new DLC includes a new horde mode where players have to survive several waves of zombies sieging the outpost.
The DLC pack isn't officially called a horde mode, but gameplay-wise is pretty similar to one. The player, a Red Talon soldier, starts out armed with the best weapons and gear and must battle seven waves of zombies in increasing difficulty. You'll also be able to play Daybreak in co-op with up to three other players.
The Daypack DLC is standalone and won't affect your progress in the main game. However, getting top scores in Daybreak will net you rewards in your regular playthrough, including the ability to recruit a Red Talon elite soldier to your camp.