Get the make and model number and check the full specifications list online. If you're buying from a store, sometimes it's a good idea to ask for a remote to check through menus on the display model. If it doesn't have a dedicated 3D button on the remote, it's probably tucked away somewhere in...
it's not being pushed as a sales pitch at the moment, just one of many features that may or may not be available. My theory is that they're deliberately letting it take a backseat to features like UHD and HDR so that when autostereoscopic 3D is ready to sell to the masses they can reintroduce...