GTA 5 DLC has leaked online -- via Steam -- but it's not the DLC you and everyone else has been begging Rockstar Games to add for eight years. At this point, it's safe to count out GTA 5 getting GTA 4-like DLC. If it was going to happen, it would have happened by now. However, while the game's single-player campaign hasn't been added to since release, Rockstar has poured a ton of content into GTA Online, and the success of GTA Online is a big reason why we are now getting GTA 5 on PS5 and Xbox Series X in an "expanded and enhanced" form. It remains to be seen what "expanded and enhanced" means, but it may have something to do with this new leak, which suggests more music is being added to the base game. The leak also suggests this next-gen update is coming to PC as well, probably for free.
Over on Twitter, Rockstar Games insider Tez2 revealed that amidst the Steam purchase-disabled mess that went down on the platform yesterday, a header image was added for one of the unknown bits of DLC added to the game last year. We still don't know what this DLC is, but the music icon in the top left corner more or less confirms it's music-related.
At the moment, no one seems to know what this could be for, but it presumably has something to do with the game's soundtrack. If so, it's likely an update with new music or remixes, and it likely has something to do with the upcoming release of the "enhanced and expanded" version of the game. Could it be for new single-player DLC? Technically, yes, but this seems unlikely.
At the moment of publishing, Rockstar Games and Take-Two Interactive have not commented on any of the information above, and it's unlikely either will as both maintain a very strict "no comment" policy when it comes to leaks and everything else of the speculative and unofficial variety. However, if any type of comment or clarification does surface, we will update the article accordingly.