A couple of trucks were spotted on the site today drilling core samples.
Also, hequals2henry used this image of Riverranchdrone's to photoshop the rendering of the building into the skyline at two different heights - 870 feet which is around where it's planned at right now, and 1,040 feet which it could end up being if the developers go ahead with it being around 75 floors. In an Austin American-Statesman article, the developers were quoted as saying that it's currently 62 floors, but that they might push it to the "mid 70s". That would put the height to around 1,040 feet tall.
870 ft
1040 ft