While exploring the open world, players can complete challenges, fight robotic enemies, and access "Cyber Space" levels inspired by previous Sonic games.

[15][16] The player explores the islands as they solve puzzles, such as orienting statues and speedrunning, to reveal parts of the map and obtain items.

[7][15][3][17] One of Sonic's objectives is to rescue three of his friends — Miles "Tails" Prower, Amy Rose, and Knuckles the Echidna — who are trapped in Cyber Space.

These either progress the story's plot (occasionally via minigames) or expand their relationships with Sonic by requesting the player to complete side quests.

[19] The player battles robots throughout the islands, all in various forms;[20] Sonic can dodge and parry attacks and use the Cyloop to make enemies easier to strike.

[23] Collecting all seven Chaos Emeralds allows the player to transform into Super Sonic, which is required to battle and defeat the game's major bosses, the Titans.

[24] Completing every island-mapping challenge and side story on each island and maxing out Sonic's stats (except for boost), or having the game's difficulty set to Hard or Extreme prior to battling Supreme, reveals a "secret" final boss fight with The End and a post-credits scene.

Doctor Eggman travels to the abandoned Starfall Islands to steal the technological secrets created by the Ancients, creatures related to Chaos.

Detecting a threat signature, Sage ceases hijacking the portal and initiates a protection protocol, dragging Eggman into an artificial dimension called Cyber Space.

Sonic, Tails and Amy investigate activity that has drawn the Chaos Emeralds to the islands, but their plane is sucked into a wormhole to Cyber Space.

Sage cautions Sonic to leave, influencing the islands' mechanical guardians and Titans to attack him, but grows to sympathize with him while observing his interactions with his friends.

Through visions of the local Koco, Sonic and his friends learn the history of the Ancients, who are revealed to be an extraterrestrial race whose planet was destroyed by "The End", an all-powerful entity.

The Titans were built to seal the End within Cyber Space, with the Ancients' essences remaining within the Koco, which become inert once Sonic and his friends help them fulfill their final desires in life.

Sonic's friends purge the corruption from him by sacrificing their physical forms, while Sage and Eggman help him collect the scattered Chaos Emeralds, allowing him to defeat Supreme.

Following his friends' sacrifice, Sonic accepts a proposal from Sage to restore them along with his cyber corruption, which he may convert into greater power to use against the End.

Returning to their holographic forms, Sonic's friends retrieve the Chaos Emeralds while he undergoes trials overseen by the souls of the Titans' pilots and the Ancients' leader, Master King.

[23] Sonic Team ultimately determined that the series' traditional linear design contained "little room for evolution"[29] and felt it could not progress in this direction.

[33] The idea to make an open-world Sonic game came from Kishimoto, who enjoyed watching the evolution of the platform genre's world map concept since it was popularized by Super Mario Bros. 3 in 1988.

[35][34] Kishimoto returned to direct Frontiers,[14] while Sonic Unleashed (2008), Generations (2011), and Forces art director Sachiko Kawamura produced it.

[23] Sonic Team chose not to raise the difficulty level as the game progresses since the open world would provide plenty of content.

[33] Iizuka noted that the story differs from previous Sonic games in that it is less humorous and does not make the player's goal obvious, instead challenging them to figure out how to solve problems themselves.

[45][46][47] "Another Story" exclusively includes both an orchestral version of "I'm Here" and a heavier remix called "I'm Here – Revisited", with re-recorded vocals by Quinn, both of which play in the revamped The End battle.

Sega originally planned to release Sonic Frontiers in 2021 to coincide with the franchise's 30th anniversary but delayed it by 1 year for quality control.

[69] Frontiers received a free DLC pack on November 14, 2022, that included additional cosmetics inspired by Capcom's Monster Hunter series as well as a cooking minigame.

[77] Kotaku felt the game looked fine but derivative and bland, lacking the series' unique identity,[17] and Polygon and Nintendo Life found the open world desolate.

[99] IGN criticized the combat in Frontiers for being repetitive and unengaging, explaining that the battles against faceless robotic enemies detracted from the fast-paced platforming gameplay.

[102] IGN and VentureBeat pointed out issues with technical limitations causing large objects to pop into view, disrupting immersion and diminishing the overall polish of the game.

[108][109][110] The Washington Post wrote that many enjoyed its controls, emphasis on freedom, story, references to prior Sonic games, and soundtrack.

[109][111] The Nintendo Switch version of Sonic Frontiers was the fourth best-selling retail game during its first week of release in Japan, with 26,067 physical copies being sold.

[118] Sage, an antagonist character introduced in Frontiers, is slated to appear as a playable racer in the upcoming Sonic Racing: CrossWorlds.