Personally I try to be covert. If I'm already deep into thr interview I'm too focused on the questions and what I'm going to say (I'm not thinking about my stutter). Since the inteview has already started I dont want to break up the flow. Imo it should be obvious you are stuttering, they should be accommodating. Just go on like nothing happened. If you feel it helps then disclose it early on. Having a script of things to say sometimes helps especially for behavioral and background questions.