Microsoft is rumored to have acquired the marketing rights to a major AAA game that has yet to be announced. While we don't know what game it is, or even what IP it belongs to, there is big reason to believe these rumors.
Industry insider Shinobi602 on Twitter claims, "So there’s a major unannounced AAA that Microsoft has marketing on. Not bad Xbox. Bring on E3."
Shinobi602 is known for accurate leaks regularly, and while no details were provided, Windows Central editor Jez Corden made an interesting claim. The marketing deal is supposedly related to the rumored Assassin's Creed Origins. This is an educated guess, according to Corden and is backed by a number of users on NEOGAF.
So there's a major unannounced AAA that Microsoft has marketing on. Not bad Xbox. Bring on E3.
— shinobi602 (@shinobi602) May 11, 2017
Nothing has been confirmed at this point, but the rumors on the next Assassin's Creed are all over, including some surfaced screenshots.