The 2023 roadmap for Sonic Frontiers reveals that Amy, Knuckles, and Tails will be made playable in a free content update coming to the game later in the year, along with some new game modes, skins, and events.
After the launch of Sonic Frontiers, Sega promised that it'd be supported with DLC for some time to come, immediately following that up with the soap shoes and a Monster Hunter collaboration. It seems that's just the start, as it's revealed a roadmap for 2023 that includes several new modes and bits of content being added to the game for free in the future.
The first content update for Sonic Frontiers will add a jukebox for listening to the game's soundtrack (seemingly in the open world too, judging by the image used), a much-needed photo mode, and some new challenge modes. No details were given on what those challenges are, but we see images of Super Sonic and Cyberspace, so they'll likely be involved.
The second content update includes new Koco to collect, an open-zone challenge mode that seems to be some kind of time trial, and something special to celebrate Sonic's birthday. Again, we don't know what these modes are going to be made up of or how Sonic's birthday is being celebrated, but it does indicate that the second content update will arrive sometime in June, as that's when Sonic's birthday is.
Finally, the third content update promises something quite exciting - a new story scenario and new playable characters. The image used for this part of the roadmap shows Tails, Amy, and Knuckles, which all but confirms that they're going to be made playable within the update. The story scenario seems likely to involve Sage, as she's shown next to the three.
It's worth noting that none of the content updates have any kind of date attached to them so far, with Sonic's birthday being the only kind of hint given for one of the updates. Although we'll have to wait and see when these updates drop, Sega did reveal that Sonic will be getting a special Christmas outfit on December 21.