A full version change, but I'm not finding anything in the way of what the new features or capabilities are. And this URL: http://www.apple.com/xsan/ still shows Xsan 2. So I'm a bit mystified what the strategy is here.
There really isn't anything new functionality wise. The big thing is that they are syncing up with more recent code from StorNEXT so that newer versions of StorNEXT can take advantage of things like native extended attributes on other platforms beside mac.