Official version of Vatikan
Vatikanstadt is currently written as Vatikanstaat. Wikipedia says the official version in Germany is Vatikanstadt, even though "Vatikan, Vatikanstadt oder Vatikanstaat" is also allowed. Since the wikipedia page title is with Stadt, i would go for Vatikanstadt instead of Vatikanstaat
Updated by Simon Schaufelberger over 5 years ago
even on their official website it is written as Vatikanstadt.