According to Sonic Frontiers game director Morio Kishimoto, the game will take 20-30 hours to complete. However, the developers have made a big bet on the open world - therefore, an impressive part of the content is optional. And to pass 100%, you will have to spend twice as much.
Despite this circumstance, Kishimoto considers Sonic Frontiers a competitor to traditional platform games, not open world games. He also promised a number of elements never seen before in a Sonic game.