Pretty sure that's been known for sometime. Isn't it based on a book of the same name about Bulger?
Gets is right, it was a working title it seemed for a while. It is "loosely" based on the book so there is no telling if it will try to be based on real life, or if there will be more Hollywood involved.
But as for the title I don't think it was for sure known until gets posted it above.
Everytime I've seen it talked about it's been referred to as "Black Mass" so either way, people have referred to the film under that name for a while. Now it's official.
