Stranger Things season 4 volume 1 was released a few weeks back. The season finale left the audience speechless with a shocking twist. Though most of the fans did not see it coming, Gaten Matarazzo somehow predicted the ending of season 4 way back in 2016.
In Season 4 "Chapter Seven: The Massacre at Hawkins Lab", it was revealed that 001 transformed into Vecna. Working as orderly at Hawkins Lab, he explains to Eleven how he ended up in the lab, confessing to murdering his family using his powers. He urges Eleven to join him but she refuses and both fight. At first, it looks like Eleven will lose, but she eventually overpowers number one.
Through her powers, Eleven sends Henry to the Upside Down. In the other dimension, he bursts into flame and ultimately becomes Vecna.
An old video of Gaten Matarazzo has surfaced online in which he states his favourite fan theory. As per that theory, Vecna was actually a test subject from Hawkins Lab. You can check out the video below.