In the book, Step 2 which is about the 810 plan it does state that.... On Step 2 it's unlikely you'll remain in ketosis as you'll be introducing a greater amount of carbohydrate to take your daily calorie intake up to 810 cal/day. The good news is that you'll still see great weight loss because your energy intake is still low.....
I never stay in ketosis when on 810, but I am not always in ketosis on SS or SS+ either.