Not sure exactly but the population has grown from 1.5 million in 2001 to 1.9 million in 2021
Some of that growth fit into existing stock but since the late 90s there has been a lot of new neighbourhoods built.
The city generally plans ahead, even building public transport like metro out before it is completely needed.
E.g. out to this new neighbourhood
https://en.m.wikipedia.org/wiki/Aspern