The next Arrowverse crossover event will take place entirely during The Flash season 8 and here's why the superhero team-up isn't happening across The CW's many series as it has in previous years. The last full-fledged Arrowverse crossover was 2019/2020's Crisis On Infinite Earths, which remade the Multiverse and merged Supergirl's Earth-38 with The Flash's Earth-1 onto a hybrid world called Earth-Prime. But after Crisis, the Arrowverse's superheroes have been confined to their individual series.
The Flash season 8 will kick off in November 2021 with "Armageddon," which will span the first 5-episodes of the series led by Grant Gustin as Barry Allen. A new alien powerful alien threat will come to Earth that will require the Flash and his wife, Iris West-Allen (Candice Patton) to enlist super friends old and new from across the Arrowverse. The guest-stars in The Flash season 8's crossover will be Batwoman (Javicia Leslie), Mia Queen/The Green Arrow (Katherine McNamara), Black Lightning (Cress Williams), Ray Palmer/The Atom (Brandon Routh), Alex Danvers/Sentinel (Chyler Leigh), and Ryan Choi (Osric Chau). In addition, supervillains Eobard Thawne/The Reverse-Flash (Tom Cavanagh) and Damien Darhk (Neal McDonough) will also be back for "Armageddon."
The reason why The Flash is hosting guest stars as a crossover-of-sorts instead of a bonafide multi-series team-up is entirely due to COVID-19 restrictions. Along with the rest of the entertainment industry, the Arrowverse shows were able to resume production in 2020 with strict COVID protocols in place, but this made it impossible to stage the kind of crossovers the Arrowverse has done in the past. An event like Crisis On Infinite Earths requires the actors and hundreds of crew members from every series to work closely together and an endeavor of that magnitude isn't possible with COVID safety measures in place. For the 2020-2021 season, the lone nod towards an Arrowverse crossover was Arrow's David Ramsey guest-starring as John Diggle in The Flash season 7 and Superman & Lois season 1.
The format of "Armageddon" will also be different from past Arrowverse crossovers. Each of the first 5 episodes of The Flash season 8 will likely feature only one or two guest stars because of COVID-19 protocol measures. Therefore, unlike Crisis On Infinite Earths, it's doubtful that fans will be able to see all of the superheroes assembled the way Crisis ended with the Justice League standing together. But, in a way, the absence of superhero spectacle is also an advantage since fewer guest stars per episode mean more time for character interactions between the individual heroes. After all, "Armageddon" will be the first time the new Batwoman, Ryan Wilder, will meet Barry Allen's Flash, so their interactions will have room to develop.
The Flash is also serving as the nexus of the next Arrowverse crossover because it's now the flagship of The CW's superhero universe. By entering its 8th season, The Flash matches the longevity of the now-canceled Arrow, the first series that kicked off the universe, and The Flash will be the longest-running Arrowverse show by the end of season 8. In addition, Supergirl ends with season 6, which leaves DC's Legends of Tomorrow as the other longest-running Arrowverse show as it enters season 7. The Flash is now the centerpiece series of the Arrowverse and it's only natural that the other heroes come to Central City when the Flash calls.
Until the COVID-19 pandemic is fully behind us, the chances of a multi-series Arrowverse crossover like in years past are nonexistent. But The Flash being able to bring aboard multiple superhero guest stars across 5 episodes for what the producers promise will be one of the "most emotional" Flash stories ever should still be something special. And, as Barry Allen proved when he jumped universes to meet Supergirl (Melissa Benoist) in 2016, the Arrowverse's superheroes don't necessarily all need to be assembled for "Armageddon" to be a memorable crossover that fans will enjoy.