The single-player campaign for Naughty Dog's Uncharted 3: Drake's Deception is free for all PlayStation 3 players, according to the game's current listing on the U.S. PlayStation Store.
The 2011 closer to the Uncharted trilogy has previously been featured as a free title for PlayStation Plus subscribers, and its multiplayer component went free-to-play last February. Multiplayer mode is still free, though Sony appears to still be charging for DLC and in-game add-ons.
Polygon has reached out to Sony to ask if this is an error and if the offer is available only for a limited time.
Naughty Dog is currently working on a new Uncharted title for PlayStation 4. The game was announced shortly before the North American launch of the PS4 last November.