"Before we start, I just wanted to let you know that I do have a stutter. If there's anything you need me to repeat or if you have any questions about it, please dont hesitate to ask; I'm pretty open about it". This is my generic opening for when I wanted to disclose. It wouldn't always be at the start of the interview or in those exact words. But that's a very standard disclosure I feel. Let's them become aware of the situation. Shows that you're comfortable with yourself and your speech. And the vast majority of the time no one has asked about it because they don't care or think it's as big of a deal as we think it is. they'll usually think, "If they can do the job and it doesn't bother them, why should it bother me?"