The CV of a Rockstar New England employee has indicated that the studio is currently working on a follow-up to one of the publisher's biggest franchises.
Spotted by Kotaku columnist Superannuation, the LinkedIn profile of senior graphics engineer Doron Feinstein lists his current project as "Next version of a famous IP".
While it doesn't specify platforms, it's probably safe to assume at this stage that this will be for next-gen consoles.
There's plenty of speculation on what "famous IP" Feinstein is referring to. The most likely candidates would be Red Dead or perhaps Bully.
However, Superannuation argues that it could turn out to be DLC for Grand Theft Auto V, perhaps in the style of GTA IV's Episodes from Liberty City expansions.
References to "next version" rule out the possibility of this being Agent, Rockstar's newest IP that was announced back in 2009. The game is apparently still in the works, although nothing has been heard since its initial announcement.