They will be self-publishing the game, following Warner Bros publishing HITMAN 2, and have announced that this will be an Epic Games Store exclusive.
This is a one-year exclusivity deal for the Epic Games Store, with the game also being released on Google Stadia and home consoles.
This has been stated again by Hakan Abrak, CEO of IO Interactive, who has said:
For our long-term fans that have supported us on the World of Assassination journey, we’re happy to have mastery and location carryover from their existing progress into HITMAN 3 on Epic Games Store.