RbxThumb is a new ContentId format that allows easy loading of thumbnails. It works everywhere you would expect image ContentIds to work including in ImageLabel.Image and ContentProvider:PreloadAsync.
The format for an RbxThumb contentId is “rbxthumb://type=[ThumbnailType]&id=[TargetId]&w=[Width]&h=[Height]”. The order of parameters is enforced.
For example, if you wanted an ImageLabel with a thumbnail of my lovely avatar on it you would set the Image property to:
Supported thumbnail types and sizes:
Type: Supported Sizes: "Asset" 150x150, 420x420 "Avatar" 100x100, 352x352, 720x720 "AvatarHeadShot" 48x48, 60x60, 150x150 "BadgeIcon" 150x150 "BundleThumbnail" 150x150, 420x420 "GameIcon" 50x50, 150x150 "GamePass" 150x150 "GroupIcon" 150x150, 420x420 "Outfit" 150x150, 420x420
RbxThumb automatically batches thumbnail requests together so loading them is more efficient. Thumbnails that are not yet ready are automatically retried up to 3 times.
For more documentation, see the rbxthumb section here: