The official description for Horizon 2 Forbidden West says “Horizon Forbidden West continues Aloy’s story as she moves west to a far-future America to brave a majestic, but dangerous frontier where she’ll face awe-inspiring machines and mysterious new threats. Coming to PlayStation 5.”
As of now, very little is known about this follow up to Horizon Zero Dawn, but do know that it's expected to launch in 2020 as a PlayStation 5 Exclusive and may even be available when the PS5 launches. The game is supposedly set some 1,000 years after the old ones fell, which would mean that 26 years have passed since the events of Zero Dawn. It's also expected that we'll see parts of the world that we've never seen before.