A “Cubase AI 8” version does not exist as such yet. LE and AI versions are only delivered with hardware devices and unfortunately it is not possible to update them directly to their successor, like the retail versions do.
Audio Projects made with Cubase AI 7 should open normally in Cubase Pro 8 and Cubase Artist 8, but not in the opposite way, especially if a “version”-exclusive feature has been used within the project.