Fassbender's company DMC Film is co-producing the film as well, teaming up with Ubisoft Motion Pictures. It's unclear which part of the game's canon will form the basis of the film, if any. Variety says the "plot revolves around a man who learns his ancestors were trained assassins after he is kidnapped by a secret org with ties to the Knights Templar, and sent back in time to retrieve historical artifacts," which sounds like a game revolving around Desmond to us. It also sounds like the basic root of the entire game franchise, so ... do with that what you will.
The new deal with Fassbender's DMC Film helps to put Ubi's previous Sony talks to bed. Talks last November apparently fizzled, though Ubi is still open to "re-discuss" things "once the production package is finalized." Ubisoft Motion Pictures will hire the project's director and writer before getting involved with any third parties – a response to the lackluster reception Prince of Persia: The Sands of Time got at the box office, which Ubi apparently attributes (at least in part) to a lack of creative control over its own property.
[Pictured: Filming of Assassin's Creed: Lineage]