According to "a person familiar with the game," it's called (either officially or internally) Assassin's Creed Victory, and it's coming to PS4, Xbox One, and PC in fall 2015.
Kotaku also reports seeing seven minutes of "target gameplay footage," which they say was produced in Assassin's Creed's engine, and thus was not pre-rendered.
In the video, the assassin climbs a tower to get a view of the city, descends, enters a carriage, and accepts a contract to kill a man. When the carriage is attacked, the assassin battles on top of the moving vehicle. The fight makes its way to a train station where the assassin ascends to the high ground, swings across the station using a grappling hook -- a new item for the series -- and takes out the target.
"It is always unfortunate when internal assets, not intended for public consumption, are leaked. And, while we certainly welcome anticipation for all of our upcoming titles, we're disappointed for our fans, and our development team, that this conceptual asset is now public. The team in our Quebec studio has been hard at work on the particular game in question for the past few years, and we're excited to officially unveil what the studio has been working on at a later date. In the meantime, our number one priority is enhancing the experience of Assassin's Creed Unity for players."
