While it might seem natural to think that Prime Rib will always be USDA Prime grade, it isn't always. This grade of meat costs more and it is hard to source. Due to this, it is often substituted with USDA Choice Grade meat. The bulk of Prime Rib sold is choice grade meat. If you want prime grade, it will likely need to be special ordered with your butcher. Keep in mind, the price will significantly increase for this cut.