For the Duffer brothers, Stranger Things marks the end of an era … sort of. Though the hit Netflix series has come to an end after nine years and five seasons, fans won’t be saying goodbye to the Stranger Things universe for good. In fact, Ross and Matt Duffer have practically said as much: There’s a Stranger Things spinoff in the works.

The Duffers have remained tight-lipped when it comes to details about the spinoff, though they have shared some insight into what fans might expect. A Stranger Things star has also weighed in, and the series finale even disclosed a crucial detail.

So, what did the Stranger Things finale reveal? And will the same cast be involved in the spinoff? Yahoo is rounding up everything we know (so far) about the Stranger Things spinoff, below.

[Warning: This story contains spoilers from the series finale of Stranger Things]

What did the Stranger Things series finale reveal about the spinoff?

In the Stranger Things series finale, we see a flashback of Henry Creel’s most painful memory when he finally enters the cave that he has long avoided. It shows a young Henry bludgeoning a scientist to death with a rock after the scientist shoots him in the hand out of fear. Henry then takes the scientist’s briefcase, which he had been shielding, and opens it to find a glowing black rock. That rock is what first awakens Henry’s powers and connects him to the Mind Flayer.

In an interview with the Hollywood Reporter about the series finale, Matt Duffer revealed that “the rock and where the rock came from” is crucial to the spinoff.

“The spinoff is not about rocks or mining the rocks, but I would say that’s the loose end that’s not tied up that will be tied up,” Duffer told the outlet. “But ultimately, and we have said this before, but I guess to reiterate, it is an entirely new mythology.”

Duffer added, “This spinoff does connect and will answer some of the lingering questions. It’s not specifically about the Mind Flayer or the Upside Down, but hopefully it provides some answers to that at least those lingering questions related to Henry’s memory.”

Will the Stranger Things cast return for the spinoff?

Fans shouldn’t expect to see any familiar faces in the spinoff series. In Screenrant, Matt Duffer said: “It relates in some ways, but it really is a completely different story and a completely different location with completely different actors and characters. So it’s its own. It’s really its own entity.”

What else do we know about the spinoff?

While it won’t follow the Hawkins gang we’ve come to know and love, the Stranger Things spinoff, Matt Duffer previously told Variety, will still be part of the show’s brand and style of storytelling, and will revolve around “kids, adventures, sci-fi/fantasy, rather than increasingly expand what could become an insanely convoluted mythology.”

“You’re starting with new characters — it’s like clean slate,” he told the outlet. “You’re not tied up into any knots. There’s something refreshing about it.”

The Duffers will be involved in “helping shepherd it along,” per Variety, but given their new Paramount deal, they won’t be the showrunners of the spinoff.

Has the Stranger Things cast said anything about it?

So far, Finn Wolfhard, who plays Mike Wheeler, is the only member of the Stranger Things cast to correctly guess what the spinoff may revolve around.

“Nobody — not Netflix, not any of the producers, not any of the directors, not any of the actors — nobody else has figured out what the spinoff is. Finn figured [it] out, which is pretty remarkable,” Ross Duffer told Variety. “We’ve mind-melded with this kid a bit.”

In Variety, Wolfhard speculated about what the forthcoming Stranger Things spinoff could be about, and compared it to another beloved cult series.

“Like David Lynch’s Twin Peaks,” he told the outlet. “Sort of an anthology and different tones but similar universe or same universe. I think set in different places and all tied together through this mythology of the Upside Down. Don’t even talk about Hawkins. Don’t have any mention of our characters. They were toying around with ideas in case Netflix wanted them. I’m sure they do, and I’m sure it will happen, but there’s nothing official. I think the coolest way, the way that I would do it, there has to be labs everywhere. If there was one in Hawkins, there’s one in Russia. Where else could they be?”

The Stranger Things spinoff was confirmed in November, when Matt Duffer told Deadline, “We are moving forward with it. Netflix, they finally know what it is. We held it. They were so frustrated. We just would not tell them. Finn guessed what it was. So he was the only one who knew.”