Standard (frequent access, no minimum), Nearline (about once a month, 30-day minimum), Coldline (about once a quarter, 90-day minimum), and Archive (less than once a year, 365-day minimum). Colder classes cost less to store and more to access.
On the ACE you pick the class by access frequency. Autoclass can move objects automatically based on actual use, and the bucket location (region, dual-region, or multi-region) cannot be changed later.
Cloud Storage classes is a concept that can show up on the exam. Check the full guide to see it in context.