The Flash season 7 premieres in 2021, but the number of episodes hasn't been decided yet. Thanks to Arrow's series finale earlier this year, The Flash is now The CW's most senior superhero show. Like all of the Arrowverse series, The Flash spent season 6 dealing with Crisis on Infinite Earths, the massive crossover that concluded in January. Barry Allen and co. spent the last portion of the season reacting to the fallout, as well as a new threat in Eva McCulloch's Mirror Master. Since The Flash season 6 was cut short due to the coronavirus pandemic, it ended on even more of a cliffhanger than usual. Eva is still at large, while Iris, Singh, and Kamilla remain trapped in the Mirrorverse.
Season 7 will wrap up those storylines first before moving on to new things. In fact, showrunner Eric Wallace revealed the premiere is already 90% filmed, due to the timing of the filming shutdown in March. Season 7 will also have to address Ralph Dibny's exit, as actor Hartley Sawyer was fired earlier this year for a series of racist and misogynistic tweets. Luckily, Wallace shared last month The Flash plans to take advantage of Ralph's ability to change his appearance, meaning his story can be concluded without Sawyer. Additionally, season 7 will reference current "societal events," with Joe West particularly affected by them. All told, it's shaping up to be an exciting season for The Flash.
At this time, though, one key part of the upcoming season remains unknown. In a recent interview with Discussing Film, Wallace revealed the number of season 7 episodes hasn't been decided yet. He explained it will depend on when The Flash is able to safely begin filming:
I’m still not exactly sure how many episodes of The Flash will get actually on the air in 2021...The hope is to start in October or November, to start in the fall. That is definitely the hope. Hopefully we’ll know more in the next couple of weeks. I’m actually very cautious, cautiously optimistic. And of course when we start, we’ll determine how many episodes we can crank out. So let’s all keep our fingers crossed for the fall.
At this point, it seems unlikely The Flash will able to do its usual 20+ episode season. The same could be said about the other Arrowverse series as well. Even if The CW decides to air The Flash and others into the summer, there may not be time to produce a full season. As network shows typically begin filming in the summertime, a 20+ episode season 7 would likely result in little to no break before filming season 8, provided the The Flash is renewed.
However, one Arrowverse show, Legends of Tomorrow, should theoretically be able to do the same number of episodes it usually does. That series typically films 15-18 a season and is already set to premiere later than The Flash, Superman & Lois, and others. Supergirl is a little more of a wild card, as it usually does a full season like The Flash. However, this season, it's been held like Legends of Tomorrow, most likely due to star Melissa Benoist's pregnancy. As Wallace stated, hopefully exact episode numbers will be determined in the coming weeks for all Arrowverse series, especially The Flash.
Source: Discussing Film