Which Sonic game was developed for the series' 20th anniversary?

Sonic Generations was developed for the Sonic series’ 20th anniversary. Released in 2011, it celebrates the franchise by bringing together two versions of Sonic and reimagining stages from earlier games.

The game’s central premise involves Classic Sonic and Modern Sonic meeting after a mysterious force disrupts time. Players switch between the two styles: Classic Sonic uses primarily 2D platforming inspired by the Genesis-era games, while Modern Sonic uses the faster 3D-oriented moveset associated with later titles. Each era receives recreated stages, including locations drawn from Sonic’s long history.

Sonic Team began discussing an anniversary project after completing Sonic Unleashed. Producer Takashi Iizuka wanted the game to showcase the best of Sonic’s past, while the split between classic and modern playstyles gave the celebration a playable structure rather than making it merely a retrospective. The game was released for PlayStation 3, Xbox 360, and Windows, with a separate Nintendo 3DS version.

Sonic Mania, Sonic Lost World, and Sonic Forces are later or differently motivated projects, so they are not the series’ 20th-anniversary game.