This email from Microsoft was sent out to customers on August 18, 2023.
The Xbox 360 Store and the Xbox 360 Marketplace (marketplace.xbox.com) will be retired on July 29, 2024.
SERVICE UPDATE: XBOX 360 STORE CHANGES
Starting July 29, 2024, the Microsoft Store on Xbox 360 and on marketplace.xbox.com will no longer be supporting purchases. This includes games, trials, add-ons, avatar items, apps, gamerpics, game trailers, and videos. It also includes purchases like gamertag changes on Xbox 360, Xbox Live Gold subscriptions, in-game purchases, and Movies & TV. Games and content purchased before that date will still play as intended and content redownloads will continue to be supported for owned content.
If you intend to redeem any codes for Xbox 360 content via your Xbox 360 console, then you will need to redeem them to your account before July 29, 2024. After that date, they may no longer be redeemable. Gift cards and subscription cards will not be impacted.
You can find the full list of backward compatible titles and DLC supported on Xbox Series X|S and Xbox One consoles at the Xbox Backward Compatibility Games Library below. These titles can still be purchased at xbox.com after July 29, 2024, and are playable on Xbox 360 consoles, too.
