My guess is that you’re doing this for weightloss and not expressly for autophagy (which can be induced in more ways than just fasting, btw). If this is the case, then you’re fine. If autophagy is the main goal, you’re better off sticking with water only.
Any drink that uses aspartame or sucralose (Splenda) is going to cause a glycemic response. In fact, Splenda has been shown to have more response than straight up eating sugar. Splenda is essentially poison. And it’s horrific that “diet” drinks are even marketed to diabetics. If you consume drinks that are sweetened by non-glycemic index sweeteners such as stevia or erythritol, you will not see a drop in ketosis.