I saw in my seller dashboard that there’s a new style of subscriptions, and my existing ones are marked legacy.
I went to my developer sandbox to experiment with the new style, and I still only have the ability to create legacy style subscriptions.
What can I do to get my sandbox updated?
It should be live now. 
I’m still seeing the old style when I try to create a new plan. Do I need to refresh something or just be more patient? 
This is fixed now and you should see the new style. Thanks for bringing this to our attention.
Confirmed, I see the new style subscription plans now. Thanks!