Arnold Schwarzenegger is currently in London, doing press for the U.K. release of The Last Stand. During a press conference, the actor confirmed that he will be appearing in Terminator 5, though he did not specify in what capacity. The actor then revealed that he is also officially attached to the Twins sequel Triplets and The Legend of Conan.
Back in April 2011, Arnold Schwarzenegger was attached to a version of Terminator 5 that Justin Lin was set to direct. A lot has happened between now and then, with Annapurna Pictures purchasing the rights from Pacificor in May 2011, followed by Justin Lin dropping out in September 2011.
The project has picked up some steam recently, with David Ellison signing on to produce with his sister Megan Ellison, and writers Patrick Lussier and Laeta Kalogridis agreeing to tackle the script earlier this month.
It is not known if Arnold Schwarzenegger will be back as the T-800 Terminator model, or if he will be playing a whole new character. Since the T-800 doesn't age, they may be using CGI de-aging effects as seen in Tron: Legacy.
The sequel does not have a director attached yet, although Justin Lin previously indicated he may return if Annapurna Pictures waits for him to complete The Fast and the Furious 6, which is set for release this May.