A compelling film Glass Onion: A Knives Out Mystery may be, but Rian Johnson is right to criticize one aspect of it: the title. Though the movie's subtitle is "A Knives Out Mystery," Glass Onion is not a direct sequel to Knives Out. The two films have key elements in common; both deal with wealth and privilege, both involve Benoit Blanc solving a murder mystery, and both are named after songs, with Knives Out's title coming from a 2001 song by Radiohead, and Glass Onion sharing its title with a 1968 The Beatles song. In a candid admission, however, Rian Johnson has criticized the Glass Onion title for its connection to Benoit Blanc's previous mystery.
Expressing his regret, Rian Johnson explained that he wanted Glass Onion to stand on its own rather than simply being perceived as a sequel to Knives Out. Though Johnson says Glass Onion is the next film in the series, he has also worked hard to make the two films self-contained, like "a new novel off the shelf every time." Glass Onion functions like a standalone novel in a mystery series, starring the same detective at the center, but requiring no prior knowledge of characters or plot points from the previous installment.
Glass Onion Didn't Need "Knives Out" In Its Title
Aside from Daniel Craig's Benoit Blanc returning, very little directly connects Knives Out to Glass Onion, so the second part of the sequel's full title feels unnecessary. The plot does not continue Knives Out's story, and no Knives Out characters besides Blanc are among the Glass Onion cast. A proper Knives Out sequel was entirely possible, especially if Blanc and Ana de Armas' Marta teamed up again, but Rian Johnson intentionally decided to make any future movies able to stand on their own, with different casts each time. Glass Onion is its own story, therefore, and does not need "Knives Out" in its title.
After Johnson's comments, it seems likely that the "A Knives Out Mystery" subtitle was added to Glass Onion to make sure audiences knew the movie was a follow-up to Knives Out. This aspect of the title, however, is not necessary to indicate that, as most moviegoers who have previously seen Knives Out can probably deduce Glass Onion is the next film in the series. Like fellow murder mystery anthology film Death on the Nile, which is a sequel to Murder on the Orient Express, the cameo-filled Glass Onion is an independent story from its predecessor, so there should be no confusion for anyone who ends up watching Glass Onion before Knives Out.
Why "Knives Out" Doesn't Work For Glass Onion
Aside from the distinct lack of connectivity between Knives Out and Glass Onion, the Knives Out title is more suited to the Harlan Thrombey case than Miles Bron's. A wheel of blades is prominent in the Thrombey mansion scenes, showing that the knives are literally out. The "Knives Out" title also better fits the previous mystery because Knives Out was about the members of the Thrombey clan at each other's throats, mostly over Harlan's money. "Knives Out" has far less relevance as a title for Glass Onion, especially since the movie features Miles' titular island resort. Glass Onion alone is a more fitting and meaningful title for the Knives Out sequel.
For Glass Onion, adding "Knives Out" to its title seems like a fairly transparent marketing gimmick. Knives Out enjoyed huge success, so audiences who see that title attached to Glass Onion would presumably be more inclined to watch the sequel. However, it can be argued that this tactic was ultimately unnecessary. There was already hype for Rian Johnson's follow-up to Knives Out, and the link between installments is obvious in the visual aesthetic and presence of Daniel Craig's Benoit Blanc, so there was no need to make the full title Glass Onion: A Knives Out Mystery. Johnson is right; the story of Glass Onion stands just fine on its own.