Yes, indeed. As major changes in the data structure have been made between Sarbacane Sunrise (or any earlier version) and Sarbacane Suite, no rollback is possible.
Rest assured, you will indeed find all your content and all the features to which you previously had access. You will even have access to brand-new features that you will be able to test freely until your renewal date.
However, as the interface has been completely redesigned, we nevertheless invite you to inform the users linked to your account of the update and to encourage them to familiarize themselves with it quickly and to discover the new features available.