It’s heavily rumored to be Adventure 3. Sonic team has been teasing it on Twitter and YouTube for awhile now.
Earlier this year a known Nintendo leaker did a blog about what he has heard Sonic team has been working on for the 30th anniversary. Said that they were working on 4 projects:
Last edited by shikamaru317 - on 08 April 2021
-New 3D Sonic. Couldn’t confirm rather or not it is actually called Adventure 3, but said that he did hear that it has Adventure style gameplay instead of boost, an emphasis on platforming and exploration over sheer speed, multiple playable characters (said he wasn’t 100% sure which but said that Sonic, Tails, and Knuckles at least were very likely). Developed in the US after Sonic Team moved there from Japan in the wake of Forces underperforming. Said that it is not a tie-in game for the new Sonic Netflix show, and that the recent voice cast revamps were not because they wanted to use the Netflix show actors in the games, but because the new Sonic Team in the US wanted to start a new chapter for Sonic.
-New 2D game. Not Mania 2, says that Sega believes that it’s best to leave fans to make fan made retro 2D Sonic games similar to Mania, while Sega themselves want to look to Sonic’s future. Said he heard it might be a new Dimps 2D Sonic with modern Sonic character designs, similar to Sonic Advance series from Dimps.
-Sonic Collection. Says that unlike recent Sega collections which focused on the more popular Sonic games, this collection would be focused on rarer Sonic titles that are currently unavailable without paying very high collector prices. Specifically mentioned Sonic Advance 1-3 and Sonic R as likely possibilities for the Collection.
-Mario and Sonic at 2022 Beijing Winter Olympics. Said that while it was in active development at the time (January), Sega and Nintendo were considering cancelling it, because they don’t want the negative PR of being associated with China currently, due to things like the Uyghur labor camps, democracy crackdown in Hong Kong, threats against Taiwan, and incursions into Japanese waters. Said they would review the game in a few months and make the final decision on rather or not to cancel it.