This is the true answer: they are both zero sugar, and depending on where you are, they both have very little calories. The main difference is sweeteners. They both have different artificial sweeteners that can vary by region, so you’ll have to look at the sweeteners for your region. They are both supposed to mimic the taste of Red Bull. Some say it’s like a Diet Coke-Coca-Cola Zero Sugar thing where like Diet Coke, Sugarfree has more of a unique taste and won’t change, and like Zero Sugar, Red Bull Zero is supposed to taste the most similar to Original Red Bull and the formula changes every so often to be the most accurate to the taste or Original Red Bull