This isn't (to my knowledge) properly documented anywhere but you can "guess" it based on other "XXX Wizard" open options OR if you use the wizard, you get source such as
Open("$DOCUMENTS/Big Class.json", JSON Settings(Stack(0)), JSON Wizard(0));
from here it is very easy test to change the JSON Wizard(0) to JSON Wizard(1) and run the source script again.
-Jarmo