While this isn't a conformation just yet, it looks like the stage they're at is short of putting pen to paper and signing the deal. Right now, negotiations are being finalised so it's looking very likely to happen, just needs someone to formalise it.
What looks to be happening is that Ubisoft Motion Pictures, the brand new Ubisoft movie studio, will be handling the production while Sony will be handling marketing and most other aspects. This is probably because Ubisoft wants to maintain creative control over the whole thing.
Call me skeptical, but i'm not interested in this idea one bit. Video game movies have a long history of either being really bad to below average, and not sticking to the source material. While I can imagine a great movie being made out of the Uncharted series, I really can't see how you can turn Assassin's Creed into a movie. The game isn't really at all cinematic, I honestly can't see how a decent movie can be made out of a game that is about climbing up buildings and exploration. I'd love to be wrong, but we all saw how average Prince of Persia was.