You guessed it, it's another Rules update. Check here for more info

derpibooru exclusive should be aliased

LemonDrop

Why would it, that tag implied that things were exclusively uploaded on Derpi, it wouldn’t make sense to alias existing instances of that tag. It would make sense though to have a new tantabus exclusive tag for people who solely upload their AI art here though, depending on how useful of information that is (might not be that important really).
Background Pony #F790
Derpibooru exclusive is for art uploaded solely to Derpibooru by its original creator. Images on Tantabus originally on Derpi were automatically imported and can’t be considered the prompter/artist’s official upload. Also, images here originally on Derpibooru will remain there as well until January 6, invalidating images that were imported by their creator.
Syntax quick reference: **bold** *italic* ||hide text|| `code` __underline__ ~~strike~~ ^sup^ ~sub~

Detailed syntax guide