It appears Developer Hangar 13 has stealth launched a PS4 Pro update via patch 1.05 (which notably added custom rides and racing) for Mafia III.
According to Digital Foundry, on the PS4 Pro the game offers a bump in resolution to 1440p on 4K televisions, along with other visual improvements, such as, motion blur, and improved shadows. Curiously, such enchantments and PS4 support are not even mentioned in the patch notes.
If you’re on a 1080p television, then you will also see an improvement, as the 1440p resolution will be down-sampled to 1080p, offering a slightly noticeably difference. However, none of these changes apply to the game’s cutscenes, which still run the launch PS4 assets.
As for the framerate, generally the game will run at a stable 30 FPS, but can drop a few frames — to around 26 FPS — during some of the most intense moments.
You can see the changes and details of the PS4 Pro support for yourself via the video below: