According to the developers, “As an independent studio, our partnership with Epic has given us the freedom to create HITMAN 3 exactly as we imagined and self-publish the game to our players directly. It’s also important to us that we honour the time our existing PC players have spent in our previous games.”
However, we should point out that the exclusivity will run for 12 months, which means that it should be available on other distribution platforms after that, presumably like Steam. Note that this exclusivity is only for the PC and that it will still release on other platforms like the PlayStation and Xbox at the same time in January 2021, along with Google Stadia as a streamable title.
IO also notes that players who have Hitman 2 on Steam will be able to import their progression to Hitman 3, as well as import locations from the other titles, so that’s some good news for players who might not want to start from scratch.