Binary!Sans is an Glitched Out!code created by True Code. He is an error created from a glitch form a now destroyed AU. He’s currently resides within the AntiVoid.
BackStory[]
In a Undertale Genocide Route, a glitch in the system made a different skeleton appear at the last corridor. That is when the Human and the glitch would make eye contact and thats when the fight begins. In this universe sans doesn't appear in the last corridor because when he was going to it a bug happened which switched sans with a different skeleton. The human would lose to the glitch and that Undertale universe would disappear out of existance killing the glitch. But. It would land into a anti-void where the glitch will somehow be able to collect itself back together with a different peersonality.