The existence of Outlast 2 was confirmed in October 2014 but it wasn't made officially official until a year later, with a teaser that hinted at a similar sort of horror in a very different kind of place. Developer Red Barrels said in the initial announcement that the sequel would not be set in the halls of the Mount Massive Asylum as the original was, and recently repeated that point in a tweet-spree in which it dropped a few more bits of info about the game.
@JrDamond No asylum this time around; we're going for a new setting.January 6, 2016
Red Barrels said that the new game will take place “somewhat after” the events of Outlast, and—no surprise here—fleeing and hiding will be a non-optional part of the experience. The tail-end of the October teaser, when the scene switched to a familiar night vision mode, suggests that the basic gameplay will cleave fairly closely to the original, but Red Barrels President Philippe Morin told Polygon that the success of the first game means the studio can take a slower and more ambitious approach to the second.
“We're in full control of what we ship and when we ship it,” he said. “For the first Outlast, we were in a rush to release the game before running out of money. Because more than 3.5 million players have played the first game, we're now in a position to make decisions based on our ambitions.”
Outlast 2 doesn't have a hard release date yet, but the studio said that it's set to come out this fall.