Arrowverse's new Multiverse. The 5-hour crossover event closed one chapter and began another for The CW's multi-franchise of DC TV shows in the final two hours. Based on the 1985 comic series by Marv Wolfman and George Pérez, Greg Berlanti's DC TV universe was forever changed as the heroes birthed a new Multiverse in the fourth hour of the crossover. The fifth and final installment began exploring the new reality, known as Earth-Prime, for all of The CW's Arrowverse series going forward.
With Green Lantern Corps and the Guardians of the Universe. However, viewers may have recognized the footage as it came from 2011's Green Lantern starring Ryan Reynolds as Hal Jordan. With Berlanti and fellow Arrowverse colleague Marc Guggenheim having co-written the film, it was the first time footage from that film was included in their DC shows.
Despite it being from the Reynolds film, the inclusion was not to make the movie part of the new Arrowverse canon. HBO Max is developing a number of DC series for the new Warner Bros.-themed streaming platform and one of them is a DC Comics president/CCO Geoff Johns, becoming the duo's second go together with the property. The footage included in the final Multiverse montage in Crisis on Infinite Earths was to set up its place with Berlanti's other DC series.
Visually, Green Lantern will have a different look and tone as the montage was simply demonstrating its existence within the Arrowverse. Similar to how all of Berlanti's DC Universe series (Stargirl) were included in the new Multiverse, that's what is happening for the HBO Max show. Moving forward, it wouldn't come as a surprise if every DC show Berlanti develops in the future for any of WB's platforms becomes part of Arrowverse's new Multiverse. Since it was announced almost two months prior to the crossover, it makes sense now why Berlanti couldn't share any details initially.
It had been most likely decided already at that point that Green Lantern would exist within the Arrowverse's Multiverse post-Crisis. The prolific TV/film producer is also developing a DC anthology series, Ezra Miller's DCEU Flash, it might be easy for the two Warner Bros. owned platforms to allow Green Lantern and the Arrowverse shows to crossover in the future.