Disclose your stutter to the interviewer beforehand so they don't jump to their own assumptions. They may admire your courage and bravery for doing so. It's the kindest thing you can do for yourself to take a lot of pressure off your shoulders than force yourself to be a fluent speaker. Don't turn it into a negative thing and don't spend too much time talking about your stutter to them (i.e. how long you've stuttered for, struggles you've faced with stuttering, etc.) - they won't care about it unless they curiously ask you and they may see it as a guilt trip. They're only here to see what skills you can offer regardless of the stutter. If you can play it off that you're confident and coping with it then they should feel the same about you. This is much better than spending hours rehearsing over and over to be a fluent speaker as it's too risky and if you end up stuttering and having blocks here and there during the interview anyway, you'll be likely to be very harsh and critical on yourself at the end.