I had my Cambridge C1 Advanced Exam last month. The results came in and I have level C2 across all the segments. Around 98% of the points for the exam. I also considered disclosing my stutter to the Interlocutor, but chose not to. My stutter is on the mild to moderate side, so maybe your case may be different. Actually the important thing is to do as many practice test for the other parts of the exam as you can.(The ones that don't require you to speak). I did around 15 test per module and on the exam date I aced all the non-speaking modules in half the time. You can see how that increased my confidence dramatically. If you are sure you did well on the other parts, then if Speaking receives a low mark - it's a no bother. You'll still pass the exam. On the actual Speaking exam, the nerves definitely got to me. But I still managed to perform better than my partner, who didn't have a stutter. I see your exam is next week, so I suggest tackling all the practice tests you can and you will be fine. Try to get a good night's rest beforehand. TLDR: Stuttering shouldn't hold you back in the exam. Just prepare intensely for the non-speaking modules. ')