Here's an updated top 40 list of Austin's tallest under construction and proposed high rises. Much of Austin's booming construction activity is for residential mid-rises and not on the list.
Virtually all of the information was obtained from press releases, city permit searches, published articles and published renderings. I use Emporis high rise standards for including projects to the list.
There are several State, University of Texas and Travis County buildings where the status and height information is not easy to obtain and may not currently be as I have listed. I probably haven't even included all of them on this list. But all of these buildings are on the low end of the high rise scale. So I don't really care.
The top three on the list all have the potential to be Austin's new tallest. If they all get built as proposed Austin will have four towers in the ~650' to 700' range which will make for a nice skyline.