These are just some renderings I found on
STG's Planning and Design Page
Not sure if they're current, abandoned, or what.
Capitol Study - Austin, TX - 200,000 sf
CBD Study - Austin, TX - 216,000 sf

This almost seems like it could be Shoal Creek Walk from a different angle. Maybe an earlier rendering, or is this a different building altogether?
Design Study XV - Austin, TX - 125,000 sf
From the third rendering, this looks to be in the block directly south of the William P. Clements State Office Building, behind the DoubleTree Suites.