In the sequence, a flashback visits Hawkins Laboratory in September 1979, as a bloody massacre unfolds.
Netflix also announced the first seven episodes of the nine-episode season will be released on May 27, with the final two episodes set to be released on July 1.
Show creators The Duffer Brothers recently confirmed episode seven and nine will be movie-length episodes.
Speaking to TheWrap, Matt Duffer said: “Seven and nine in particular are movies. And nine is a long movie.”
Asked about the length of episode nine, Ross Duffer said: “We’re still refining it but we will say that it is over two hours. It’s a big one.”
A synopsis for season four reads: “It’s been six months since the Battle of Starcourt, which brought terror and destruction to Hawkins. Struggling with the aftermath, our group of friends are separated for the first time – and navigating the complexities of high school hasn’t made things any easier.
“In this most vulnerable time, a new and horrifying supernatural threat surfaces, presenting a gruesome mystery that, if solved, might finally put an end to the horrors of the Upside Down.”
Speaking to NME, Matt Duffer confirmed he and Ross have an end in mind for the fifth and final season. “We do have an end. I’m sure a lot of it’s going to change, but now [it’s] the end.
“It’s just one of those things that you come up and you go, ‘That’s it, that’s right, that’s inevitable – that’s what it has to be.’”