Well.. what we saw from the game was only a tiny piece so it might have some bugs that occur in other parts of the game.
I think to remember somebody saying September, but i'm not a hundred percent certain to be honest. The game looked pretty bug-free and reasonably balanced already though. So it seems like a pretty realistic date.
I asked a guy from Yager for something like an "release date" for the Alpha... He said it might be some weeks or some months but surely this year