You might remember that back in October, Sony said that the entire Xperia Z line-up would be getting the Lollipop update. That means that the graybeard of the group, the Sony Xperia Z, will also be updated. It's hard to believe that it was just two years ago when that model wowed us at CES with its ability to emerge from a dunking unscathed.
As for the Sony Xperia Z4, most likely we will see it in Barcelona for MWC 2015. By then, those with the Xperia Z3 should be happily showing off the Lollipop build of Android on their phone.
Sony Xperia Z3