Definitely just let them know. I sometimes say “hey just before we start I just want to let you know I have a stutter, it’s not because I’m nervous, it’s purely a physical thing. If you have any questions about it I’m happy to answer” I don’t want blow my horn but I think letting them know it is not a nervous thing is a big deal. And often I’ve found with admissions-type people, putting something out there like that also scores some major brownie points. You’re gonna crush the interview!