Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
The only part of Mavericks that would be in beta would be the 10.9.x releases that have not been released - although I don’t think there are any right now.
 
It's for sure not in "Beta" anymore, but if you look at it. Mavericks isn't "done" yet, still bugs to be worked out. But with something big like a OS, you'd expect that.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.