A PS3 game, indeed.
The Last Guardian has had one of the longest, most protracted development cycles in history, originally starting out as a PS3 game before going missing in action for the better part of a decade, and then re-emerging as a PS4 game. That fact is actually reflected in how big the game’s final file is going to be- according to a tweet made by someone who got their hands on a physical copy of the game early, the final file size for The Last Guardian is just 15GB.
The person also notes that the case for the game lacks a PS4 Pro icon, which may indicate that PS4 Pro enhancements have been delayed, and will be added later down the line as part of an update of a patch. Do remember, however, that for now, that remains unconfirmed.
The Last Guardian is due to (finally) release exclusively for PS4 on December 6.