Horizon: Zero Dawn was a massive success for Sony, earning selling over 10 million units worldwide and releasing to widespread critical acclaim. Considering its success, it's a no-brainer that Sony would pursue a sequel, and if a supposed "leak" is anything to go by, that sequel will come in 2021 as a PlayStation 5 exclusive.
This leak comes from a Pastebin post originally written this past December that was just recently discovered by the Internet. The post claims to be from a third-party European developer with knowledge of the PS5, though the supposed leaker doesn't provide any evidence to back their claims. Even so, the notion that Horizon: Zero Dawn 2 could come in 2021 as a PS5 exclusive is one of the more believable claims made in the post.
There are a few reasons why a Horizon: Zero Dawn 2 release date in 2021 is easy to believe. For one, we know that Guerrilla is working on an RPG, and so far the only RPG the studio has made is the original Horizon: Zero Dawn. It would be a bit odd for the studio to jump into yet another new IP already when it just established the world of Horizon: Zero Dawn, as opposed to capitalizing on the first game's success by releasing a sequel as soon as possible.
Secondly, this isn't even the first time that we've heard of a potential Horizon: Zero Dawn 2. Voice actor Janina Gavinkar has already teased that Horizon: Zero Dawn 2 is in development. "It's incredible, wait 'til you see the sequel. You're gonna die - I know some secrets! You're gonna die," she said.
And finally, it would make the most sense for Horizon: Zero Dawn 2 to launch on PS5, which itself isn't expected to release until 2020 at the earliest. Sony appears to be somewhat slowing down support for the PS4, at least in regards to the projects its first-party studios are making, with The Last of Us: Part 2, Ghost of Tsushima, and Death Stranding expected to be the swan songs for the aging console. Sony is actually skipping E3 this year because it doesn't have much to show, which could be further indication that the company is shifting its studios' focus to the PS5.
While this particular leak isn't necessarily credible, a 2021 release date for Horizon: Zero Dawn 2 still makes some sense. Perhaps we will get our first glimpse of the game whenever the PS5 itself is announced.
Horizon: Zero Dawn 2 is rumored to be in development as a PS5 exclusive.