They didn't announce it specifically to my knowledge, but for sure they are using Miku NT and Meiko NT, because they said they were using their new voices with them for the Pocari/Miku Symphony stuff (Meiko's talking debut for her anniversary) for them.
For Miku NT, they have been using it for every single collab talking video since 2018 (
Talking: Pocari Sweat, Shinkalion, commercials for Magical Mirai stuff, collab with Sony, STV,
Singing: Tokyo 150, rap collab, Pocari Sweat, etc) even though she was in ALPHA stages when it first got debuted on Shinkalion. This is definitely being used with Project Sekai and can't be refuted.
We know they are using Meiko NT for talking collabs along with Miku because Wat said so. Her Cherry Pie voice was used as early as October 2019. Why would they suddenly stop using it? I think it would be hard to say they're not using it for Project Sekai.
Luka's talking was used in a pop-up store last year in addition to singing with it at Kawasaki Jazz.
We saw in photos that the Kagamines were listed on the
Cherry Pie poster presentations as usable voices to get your voice converted to. So it exists and was used privately at least, why else would it be on the poster?
So wouldn't it only make sense that ALL Cryptonloids are using NT? Each character has the same type of realistic intonation, how else would they do it? Dust off VocaListener? Tuning talkloid by hand is extremely time-consuming. I don't know why people think it's so unrealistic for them to use alpha versions of Kaito and the Kagamines and the others when they used Miku NT in her alpha stages since 2018 (it's 2021 now and even though she's in beta, they still are using it!).
The point of the NT voices is for virtual idol activities to save time tuning and so Wat wouldn't get inflammation in his hands anymore. Shinkalion Miku sounded horrible, but they used it anyway, so I think using an alpha voice wouldn't stop Crypton. They said everyone had deep learning patterns around July of last year and that they were progressing on updating all of the voicebanks from the past and each Vocaloid was mentioned at one point (ex: Wat saying he was moving on from the Kagamines and Kaito).
This is my thinking on it and nobody has to agree with me, but I think it would take a lot of convincing to make me think they aren't using the NT voices.