At E3 2017 Sony and Guerrilla Games Announced that Horizon: Zero Dawn will get getting The Frozen Wilds Expansion later this year. The DLC will not be standalone so you will need the Horizon: Zero Dawn game to play this.
Beyond the northern mountains, the borderlands of the Banuk tribe challenge all who dare enter to survive the extremes. But now this frozen wilderness harbors a new threat, and for Aloy, a new mystery – one she’s determined to solve.
The Frozen Wilds contains additional content for Horizon Zero Dawn, including new storylines, characters and experiences in a beautiful but unforgiving new area.