Answer: Maltitol is not keto, as it will spike your blood sugar.
Maltitol is a sugar alcohol that appears in many products that advertise themselves as sugar-free, such as Russel Stover Sugar-Free Chocolate.
The glycemic index of maltitol is 36, which means that it significantly raises your blood sugar level. For comparison, sucrose (table sugar) has a glycemic index of 65, so maltitol isn't much better than normal sugar.
Avoid products that contain maltitol even if the label lists a low carb count, as the high glycemic index can boot you out of ketosis.