Returning as series regulars are Winona Ryder, David Harbour, Millie Bobby Brown, Finn Wolfhard, Gaten Matarazzo, Caleb McLaughlin, Noah Schnapp, Sadie Sink, Natalia Dyer, Charlie Heaton, Joe Keery, Cara Buono, Maya Hawke, Priah Ferguson, Matthew Modine and Paul Reiser, while Brett Gelman was promoted to series regular after recurring in the previous two seasons.

Eddie Munson, leader of the Hellfire Club, Hawkins High School's Dungeons & Dragons group, becomes a prime suspect in the murders after senior cheerleading captain Chrissy Cunningham dies in his trailer.

Dustin Henderson, Lucas and Erica Sinclair, Max Mayfield, Steve Harrington, Nancy Wheeler, and Robin Buckley begin investigating to clear Eddie's name.

[17]Matt Duffer indicated one of the plot's "broad strokes" is the main center of action being moved out of Hawkins, Indiana, for the majority of the season, a series first.

[17] The Duffers later expanded on their previous comments, saying that "epic" triptych structure of the fourth season was one of the main contributing factors to its exaggerated length.

[24] They likened it to the HBO series Game of Thrones in terms of its sheer scale, runtime, and newer, more mature tonal shift, as well as having split their characters across multiple distant locations.

[24][25] Another contributing factor to the show's newfound extended length was the expressed goal of the Duffers to finally provide answers to uncertainties regarding the series' long-simmering mythology, which they have been slowly revealing like "layers of [an] onion" over the past three seasons.

Halfway through writing the fourth season, Matthew and Ross realized they were going to need a ninth episode to include all of their desired plot points, which Netflix in turn "quickly approved".

[28] The character of Eddie Munson is based on Damien Echols, one of the West Memphis Three who was wrongly convicted in 1994 of the deaths of three boys due to his appearance, which residents tied to being part of a satanic cult.

[34] On November 20, 2020, Jamie Campbell Bower, Eduardo Franco, and Joseph Quinn were cast as series regulars while Sherman Augustus, Mason Dye, Nikola Đuričko, and Robert Englund joined the cast in recurring roles for the fourth season;[12] Englund, best known for portraying Freddy Krueger in the Nightmare on Elm Street films, had approached the Duffers for a role in Stranger Things, which fit well with the direction they wanted to take this season.

[25] On June 9, 2021, Amybeth McNulty, Myles Truitt, Regina Ting Chen, and Grace Van Dien joined the cast in recurring roles for the fourth season.

[36][37] In February 2020, it was announced in a joint statement from the Duffer Brothers and Netflix that production had officially begun on the fourth season[6] in Vilnius, Lithuania, at the recently decommissioned Lukiškės Prison[38][39] as well as Kyviskes airfield.

[51] The same month, Joe Keery, Sadie Sink, Natalia Dyer, Maya Hawke, Priah Ferguson, and Caleb McLaughlin were spotted filming a scene that involved buying weapons from a store.

For example, the season's major threat from the Upside Down, a humanoid creature called Vecna, was "90% practical", which the Duffers found created a better presence on the set for the actors to respond to rather than a prop for later computer-generated effects.

[36] Gower designed Bower's Vecna costume with "anemic" skin whose integration with the toxic environment of the Upside Down was apparent through the inclusion of "lot of roots and vines and very organic shapes and fibrous muscle tissue.

[60] Both volumes of the original soundtrack album for the fourth season, titled Stranger Things 4, were released digitally on July 1, 2022, via Lakeshore and Invada Records.

[66] Kate Bush's "Running Up That Hill" is featured multiple times during the season, including as part of the key scene in episode 4 with Max escaping from Vecna.

[69] Metallica's "Master of Puppets" was prominently featured in the season finale when Eddie played its guitar riffs and solo as music to lure and distract demobats in the Upside Down.

[71] Other songs featured in the season, such as Dead or Alive's "You Spin Me Round (Like a Record)", Musical Youth's "Pass the Dutchie", and Falco's "Rock Me Amadeus", also saw increased streaming playbacks of around 1,784 percent.

[6] On October 2, 2020, the show's various social media accounts posted two photographs from different sets: A poster for a pep rally hanging in a hallway at Hawkins High, and a clapperboard in front of a grandfather clock in the Upside Down, a scene that was first depicted in the season's initial teaser trailer.

[86] On July 1, 2022, after the second volume of the season was released, Netflix's website reportedly crashed due to server overload as vast numbers of users logged on to stream the new episodes, overwhelming the service.

[91] With its fourth season, Stranger Things became the second Netflix title to reach more than one billion hours viewed within its first 28 days of release, following Squid Game.

The site's critical consensus reads, "Darker and denser than its predecessors, Stranger Things' fourth chapter sets the stage for the show's final season in typically binge-worthy fashion.

"[1] Tilly Pearce of Digital Spy also rated it a 4 out of 5 stars and said "Stranger Things continues to be the beautifully addictive nostalgic thrill ride we know and love.

"[99] Tara Bennett from Paste gave it a score of 8.1 out of 10 and wrote, "There’s a lot to love about Stranger Things Season 4, especially when it comes to some of the character progression and the change in vibe which fully embraces the tropes of the best of ‘80s horror.

[102] Sophie Gilbert of The Atlantic was more critical, calling the season "a 13-hour-plus behemoth that added Wes Craven to its mood board but otherwise ended with undeveloped characters and obvious but superficial allusions to contemporary crises.

From his traumatic childhood as Henry Creel to the abusive experiments he went through as One and finally to his role as the Mind Flayer’s top general, Vecna is the perfect villain to pit against Eleven.

"[105] Vulture's Devon Ivie wrote, "[Bower] has the distinction of embodying three characters, each more unsettling than the last, as the episodes unfurl: a friendly Hawkins Laboratory orderly; Henry Creel, aka "One"; and the most significant villain of the series thus far, Vecna.

"[108] TVLine gave Sadie Sink an honorable mention on June 4, 2022 for her performance in the episode "Chapter Four: Dear Billy", writing: "Sink not only nailed the tasks [of Max trying to put on a brave face for her friends despite being anxious and afraid] while still maintaining the edge that her character had received upon enrollment in the school of hard knocks, she also played Max's bittersweet monologue to her late stepbrother with a mixture of sincerity and regret that all but defined the word 'heartbreaking'.

Later, when 'Jane' was offered a chance to rewrite history, in a manner of speaking, Brown beautifully, wordlessly played the emotions that were roiling inside of her alter ego.