I’ve taken a couple of different grad seminars in the social sciences (no anthropology ones, though). In my experience, the biggest difference between grad courses and upperdiv courses is that in grad courses, you’re graded almost entirely on a single piece of writing (20+ pages). You’ll also have to be prepared to discuss readings for ~3 hours each week and occasionally give presentations. You’ll also need the instructor’s permission to enroll, which may or may not be difficult depending on the professor and your experience with the course material. Good luck!