The series was renewed for a sixth season by The CW on January 31, 2019, along with a 22-episode order. In March 2019, it was announced that Eric Wallace would replace Todd Helbing as showrunner for the season.
Writing
The season is split in two-halves, each having their own self-contained Big Bad story. Each half is referred to by the producers as a "Graphic Novel", with the first one being titled "Blood and Truth". The split was done to avoid inducing fatigue by keeping one Big Bad for 22 episodes, as previous seasons had done. Wallace felt episode 19, which became the season finale because of the COVID-19 pandemic, worked in the series' favor because it had "a big cliffhanger" that was "a good pause point". The remaining three episodes, which had been written, will become the first three episodes of season seven. Wallace conceded there may be a few small adjustments made based on how the pandemic would affect shooting, but said Eva McCulloch’s story "is on a very specific trajectory that we want to honor and finish." Wallace continued that he thought having these three episodes start season seven was "making it stronger because it's forcing us to look at these two separate things — which is the end of Eva's story and the beginning of the next villain's story and how he relates to Barry and Iris —" and making a strong connection between them.
Casting
Main cast members Grant Gustin, Candice Patton, Danielle Panabaker, Carlos Valdes, Hartley Sawyer, Danielle Nicolet and Jesse L. Martin return as Barry Allen / Flash, Iris West-Allen, Caitlin Snow / Frost, Cisco Ramon, Ralph Dibny / Elongated Man, Cecile Horton, and Joe West. Tom Cavanagh also returns as a regular, portraying Nash Wells, another doppelgänger of his character Harrison Wells. Cavanagh also returns as Eobard Thawne / Reverse Flash. Valdes also portrayed Cisco's Earth-19 doppelganger "Echo" in the episode "Kiss Kiss Breach Breach". Sendhil Ramamurthy was cast in a recurring role as Ramsey Rosso / Bloodwork, the Big Bad of the season's first half. Efrat Dor appears as a series regular in the second half of the season as Eva McCulloch.
Design
The season introduces a new Frost costume which has a more vibrant blue color scheme than the older costume, exposes the shoulders and features a chest emblem shaped like an ice crystal.
Filming
Production for the season began on July 2, 2019, in Vancouver, British Columbia, and was expected to conclude on April 6, 2020. However, on March 13, 2020, production was shut down due to the COVID-19 pandemic. 90% of the planned 20th episode was filmed by that time, with one more day of filming anticipated to complete it; the remaining two episodes were not filmed.
Arrowverse tie-ins
At the end of the 2018 Arrowverse crossover "Elseworlds", the follow-up crossover was revealed to be "Crisis on Infinite Earths" based on the comic book of the same name. The crossover took place over five episodes–three in December 2019 and two in January 2020.
Release
Broadcast
The season premiered on October 8, 2019, in the United States on The CW. It was set to run for 22 episodes. As of March 2020, the final completed episode, before production was halted because of the COVID-19 pandemic, was to air on May 12, 2020 and once production would have resumed, the remainder of the season would air later in 2020. However, the nineteenth episode was later announced as the season finale.
