Season 4 of Netflix's hit sci-fi series Stranger Things, which was forced to delay production several times due to the coronavirus pandemic, does not have an official release date yet. But that hasn't stopped diehard fans from theorizing about what might go down when the series returns.

How many other children did Hawkins Lab experiment on? Has the gate to the Upside Down been closed for good? Did Robin and Steve get jobs at the video store? Only time will tell on those vital matters, but here are some things we know for sure about the next season. Obviously, *spoilers* for all aired episodes of Stranger Things abound.

1. Hopper is alive!

Netflix released the first teaser for Stranger Things's fourth season on Valentine's Day 2020, which confirmed what many fans have hoped for since the conclusion of the third season: Chief Hopper is alive! The post-credits scene of the last season took viewers to a Russian prison, where one prison guard references an American prisoner before feeding another very unlucky captive to the Demogorgon. The moment had fans hoping that Hopper had somehow survived the explosion that closed the gate to the Upside Down, and the video confirmed the suspicion that Hopper is indeed alive. However, it seems he is imprisoned at some type of labor camp, and we have yet to learn how his storyline will connect back to the rest of the characters.

2. We'll learn more about Hopper's past.

David Harbour in Stranger Things season 3.Netflix

During a panel at Comic Con Liverpool, David Harbour told fans that the next season of Stranger Things will reveal secrets from his character's past. He explained, "In Season 2, Eleven goes into the basement of the cabin and there’s five boxes, one of which is has stuff from Hawkins Lab, one of which says ‘Dad,’ one of which says ‘Vietnam,' one says ‘New York’ … so there are three things that we’ve established in this scene and if they don’t pay off that means that [the Duffer Brothers] are bad writers … I know specifically that in season 4 we will give you a big, huge reveal about Hopper’s backstory."

3. One minor character may be returning.

Ross Partridge attends the 2016 premiere of Netflix's Stranger Things in Los Angeles.David Livingston/Getty Images

In March 2020, Netflix released a video on showing the cast of Stranger Things gathering for a table read of season 4. At one point in the video, Ross Partridge can be seen. If that name doesn't sound familiar, he is the actor who plays Lonnie Byers, Joyce's estranged ex-husband and her sons' absent father. Lonnie hasn't made an appearance since the first season, so it will be interesting to find out why he has returned.

4. Parts of season four were filmed in New Mexico.

Millie Bobby Brown and Sadie Sink in Stranger Things.Netflix

According to Collider, parts of Stranger Things's fourth season were filmed in New Mexico. The location shift makes sense, as the end of season 3 saw the Byers family moving away from Hawkins with Eleven. Stranger Things is set in Indiana but primarily filmed in Atlanta, Georgia, so it's possible that New Mexico is just a new filming location and not the new fictional setting. Nonetheless, it makes you wonder where Joyce, Will, Jonathan, and Eleven will be moving to, and how it will affect the dynamic between the characters left behind in Hawkins.

5. Some of Stranger Things Season 4 was filmed in Lithuania.

David Harbour in season 3 of Stranger Things.Netflix

Harbour got to spend some time shooting outside of the U.S. for season 4. The production filmed part of the season in Vilnius, Lithuania, including scenes at Lukiškes Prison—an imposing looking structure that first opened in 1837 and operated until 2019. It's now open for public tours (and, apparently, TV and film production).

6. Stranger Things is about to get a lot "scarier."

Maya Hawke, Joe Keery, and Gaten Matarazzo in Stranger Things.Netflix

Joe Keery, who plays Steve Harrington, talked to with Total Film Magazine about the upcoming season of Stranger Things in 2020. “Oh man, it’s pretty amazing—the Duffer brothers have really done it again,” Keery said. “I think that this year—and I know I say this every single year—but this is definitely going to be a lot scarier than prior years, because last year was pretty dark.”

7. The first episode is titled "The Hellfire club."

Sadie Sink, Noah Schnapp, Millie Bobby Brown, Finn Wolfhard, and Caleb McLaughlin in Stranger Things.Netflix

A reported by The Independent, the Stranger Things writers have revealed the title for the first episode of season 4: "Chapter One: The Hellfire Club." Sounds ominous! The episodes after that (which are also classified as chapters)? "Tick Tock Mr. Clock" and "You Snooze You Lose."

A version of this story ran in 2020; it has been updated for 2021.