According to an announcement from Microsoft Studios and Remedy Entertainment, Quantum Break game will be available as a both Steam digital download as of September 14th. Currently, Microsoft will offer Quantum Break: Timeless Collector's Edition and Windows Store version, both available for US $39.99, or $40 as we call it.
Both Steam and the retail version will include all the latest updates.
Microsoft also notes that it will release a special retail edition of the game called Quantum Break: Timeless Collector’s Edition which will sell for €39.99/US $39.99. The retail version will also include "premium packaging", 5 game discs, making of blu-ray and book, soundtrack audio CD, two posters and quickstart guide.
It appears that Microsoft's choice to push for Windows Store exclusive games is not exactly working out, so some other and future games might be coming to Steam as well.