The patch is already available. Those who've updated are playing v1.02.
16km/6miles square.
EDIT : my bad, it's 3x3km 1.62x1.62 miles according to thedev blog.
Here some datas to compare :
http://gaming.wikia.com/wiki/List_of_largest_game_worlds
You were actually right the first time, haha. That blog post was published before the game was expanded to cover the first two of the three planned acts.