Spoilers follow for Stranger Things Season 5, Vol. 2.

In the Season 5 episode of Stranger Things, "Chapter Six: Escape from Camazotz," Dustin (Gaten Matarazzo) lays out for the Hawkins gang (and the audience) exactly what’s going on with the Upside Down. Per Dr. Brenner’s journal, all of the chaos comes down to a wormhole that’s been acting as a bridge between Hawkins and Vecna’s machinations.

If you’re an observant viewer, there have been plenty of breadcrumbs leading to this reveal, including earlier in Season 5 when Mr. Clarke (Randy Havens) was teaching his science class about wormholes. In an interview with IGN, series creators Matt and Ross Duffer said they committed to that idea going all the way back to Season 1 when Netflix required that they outline their endgame for the series.

The Duffers Have Known How Stranger Things Ends for Years

The brothers have previously said that they've known what the final scene of the show will be for "six or seven years." And it sounds like many other elements of the show's final season have been in the works even longer than that.

“Netflix came to us very early on in the writing of Season 1 and were just asking to explain some mythology,” Ross said. “We said, ‘Well, we don't want to tell the audience everything in the first season.’ It's really from the point of view of the characters, and we wanted a mystery. And they said, ‘That's great, but for us, you write it down.’”

Ross told IGN that they sat down with their writers’ room, and that’s where they developed the wormhole underpinning: “It wasn't called The Abyss then, but the idea was that there was this other dimension that all of the evil and our Demogorgons and our monsters came from. It's been in the works for a while, so it's nice to finally be able to reveal it at last.”

Netflix said, ‘That's great, but for us, you write it down.’

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Asked if the complexity of the various high-concept ideas about the Upside Down, The Abyss and the science of it all ever broke their brains, Matt admitted, “Sometimes it does hurt your brain. I'm not gonna lie.”

But he also pointed to their talented writers, especially Paul Dichter who has been with the series since Season 1. Matt said Dichter has the “superpower” of being a sci-fi expert.

“He's read every single hard sci-fi book in the world. Ross and I have not,” Matt chuckled. “He's very smart in areas like this, so he's able to keep all of this in his brain. And so whenever we get confused or the other writers get confused, Paul sets us straight.”

Another key collaborator from the start is executive producer/director Shawn Levy who helped them close out the series. In fact, for the first time in the history of the show, they co-directed an episode together, "Chapter Seven: The Bridge."