A sentence needs a subject and a predicate to make sense. With you as an understood subject (because it is an imperative), we can easily make a one-word sentence with a one-word predicate:
Some think this is cheating as there is still a subject—you—that isn’t written. The word count is one written and one unwritten/understood word. With this idea in mind, using two words is the shortest sentence you can make in English; however, “you go” by letter count is not the shortest.
Therefore, the shortest non-cheating sentence would be: