2026's Biggest Horror Sleeper Hit Officially Arrives on Streaming

If you found a mysterious doorway in the basement of a furniture store, the sensible response might be to tell the building inspector. Or call the police. Or just do absolutely nothing. Pretend you never saw it. Don't even think about walking through. That's a common sense response, but then horror movies wouldn't be very long if people behaved sensibly.

A24's Backrooms has officially arrived on HBO Max, with Kane Parsons' feature directorial debut joining the streaming service on September 25. The sci-fi horror movie became one of 2026's biggest hits after turning a viral internet sensation into a box-office phenomenon, ultimately earning roughly $350 million worldwide and becoming A24's highest-grossing movie.

The set-up is fairly simple. There's a basement in a furniture store, and a weird doorway suddenly appears. Go through it, and you find a whole host of interconnected spaces where reality doesn't behave properly, time bends, exits aren't exits, and you get the feeling you're not alone down there.

The movie features Chiwetel Ejiofor (12 Years a Slave) as Clark, Renate Reinsve (The Worst Person in the World) as Mary, Mark Duplass (The Morning Show) as Phil, Finn Bennett (True Detective) as Bobby, Lukita Maxwell (Shrinking) as Kat, Avan Jogia (Zombieland: Double Tap) as Naren Warne, Krista Kosonen (Beforeigners) as Nora, and Katharine Isabelle (Ginger Snaps) as Robin.

How Good Is 'Backrooms'?

Backrooms currently holds an 86% critics' score on Rotten Tomatoes from more than 300 reviews, alongside a 74% audience score, with special praise going to the movie's atmosphere, performances, sound design, and its ability to maintain the deeply uncomfortable feeling that made Parsons' original videos work without simply stretching a YouTube video across two hours. Collider's Aidan Kelley described it as a "near-flawless horror film", adding:

"Whether you're a fan of the miniseries or are just discovering Kane Parsons' wildly successful franchise for the very first time, Backrooms is a door that any horror fan should absolutely walk through."

Then audiences actually turned up. Backrooms opened to a staggering $81.4 million, giving A24 its biggest opening weekend ever and scoring what Rotten Tomatoes described as the biggest debut ever for an original horror movie. Its eventual worldwide haul pushed it past every previous A24 release, while Parsons became the youngest filmmaker to direct a movie that reached No. 1 at the worldwide box office.

Backrooms is streaming now on HBO Max.