Won't be open prior to June 1st and then it depends on the weather. I went last year in early June and was watching the webcam to see when it opened. Have a look at this http://webcam.popso.it/stelvio.php?PASSOEST which is a view at the top of the pass.
Dave
Stelvio pass good to say you have been but nothing special much nicer passes .Was there last year road surface very poor . blackpool like gift shops at top ... nice bar
When does the Stelvio and other similar passes in the area typically close?
I have an outside chance of a visit to Torino in September.