"Sonic Superstars" exclusive Modern Amy costume available for Steam only from Oct 10th to Oct 24th
Thankfully, that has changed and starting on October 10th when SEGA themselves updated their Newsletter webpage to add a Steam option for the subscription, but not without a caveat for Steam users.
Players wishing to get the game and the exclusive costume through Steam will only have the possibility of getting it through a limited time compared to the other options. The Newsletter page itself was properly updated with the new Steam option, but alongside it there's a note with the following message:
Sonic Superstars Newsletter said:Please note that you can only sign up to receive the in-game content on Steam from October 10th, 2023 to October 24th, 2023.
It's currently unknown why SEGA would limit only the Steam release to this limited time frame, but in the meanwhile, Steam users interested in both purchasing Sonic Superstars through Valve's store and getting this exclusive Amy costume will have subscribe to the Sonic Superstars Newsletter from Oct 10th through Oct 24th.
Subscribing to the Newsletter should get a verification email to confirm the account, but the details on how to get the in-game content haven't been received as of the time of writing.
"Sonic Superstars" is just some days away from release, with the game releasing on October 17th, 2023 on multiple platforms.
Sonic Superstars Newsletter