For rare prime rib, the in-oven temperature should be 105-110 degrees. For medium rare to medium prime rib, the in-oven temperature should be 110 to 115 degrees Fahrenheit. For well done prime rib ...
Prime rib, also known as standing rib roast ... inserted into thickest portion of rib roast registers 115°F for medium-rare, 2 hours to 2 hours, 20 minutes, or to desired degree of doneness.
The beef is flavorful enough on its own, so be light-handed with any bold seasonings and cook it no more than medium. Food & Wine's guide to prime rib has recipes to satisfy every diner.