AMD send out a short statement to announce that GTA V is part of the AMD Gaming Evolved program and that the game supports its Contact Hardening Shadows technology :
AMD is proud to welcome Grand Theft Auto V from Rockstar Games as the newest addition to the Gaming Evolved family. We’ve been working closely with our friends in Toronto, Canada and Leeds in the UK, and as part of that collaboration the game features AMD’s Contact Hardening Shadows (CHS). This technique dynamically hardens or softens a shadow’s edges depending on the distance of the shadow from the light source and object casting that shadow. This means softer shadows that diffuse more realistically. To enable CHS in the game, simply select AMD CHS from the ’Soft Shadows’ drop down menu.
Meanwhile, NVIDIA touts the GeForce-specific optimizations in GTA V over here at the GeForce blog. This includes NVIDIA GameWorks Percentage Closer Soft Shadows, which seems similar to AMD's Contact Hardening Shadows:
As you can see from Rockstar’s trailer, Grand Theft Auto V’s Los Santos and Blaine County have received an extra layer of polish for their PC outing, and with NVIDIA GameWorks Percentage Closer Soft Shadows (PCSS) you can improve fidelity further still. PCSS, if you’re unaware, introduces shadows that progressively and smoothly soften as the distance from the casting object increases, as in real life. For example, the shadow from the trunk of a tree will be sharp, and the shadows on the leaves seen some distance away will be soft.