Ubisoft has confirmed that Assassin's Creed Valhalla will only be available on one third-party store for the PC, the Epic Games Store. The game will also be launching on Ubisoft's Uplay, Google Stadia, Xbox Series X, and PlayStation 5 this Holiday 2020. It will be the first mainline new installment of Assassin's Creed that will skip Steam at launch.
Ubisoft has been avoiding Steam because of its business model. Chris Early, the company's vice president, has told the New York Times before that they consider Steam's business model as "unrealistic." That it "doesn't reflect where the world is today in terms of game distribution." Steam keeps 30% of game sales, while with Epic, developers get 88% of revenue back.
Ubisoft and Epic have an ongoing publishing deal for its titles. The first game released on the Epic Games Store exclusively was The Division 2. That game was never released on Steam, but we aren't sure if the deal extends to this new Assassin's Creed game.
Source: GameSpot