This will be a timed-exclusive, meaning that IO Interactive will be able to release the game on other distribution platforms, if they choose too, after the agreed-upon exclusivity timing. It is most likely a year, so if you plan on purchasing the game on Steam, you will have to wait until at least January 2022.
Epic Games will also be giving out the first game of the series, Hitman, this upcoming August 27th through September 3rd. This is great for those who have not had the chance to play any games in the series or for those who want to replay the game on the PC without having the shell out cash for it.
Hitman 3 will be released January 2021 for the Xbox One, Xbox Series X, PlayStation 4, PlayStation 5, PC via the Epic Games Store, and Google Stadia.