Open beta will be 9/6 - 9/13. It will be version 1.5, the 3 GB patch or 9.3 GB full download is now live.
http://na.aiononline.com/en/news/ope...-download.html
The game comes out 9/22
But if you preordered 9/18 you can reserve your name and server and start playing 9/20 before everyone else.