The PlayStation 4 Pro is a beefier console than the non-Pro version. That is true of its physical size and more importantly it is true of the hardware inside. Rather than let the hardware upgrades go wasted on existing games that have not been patched to utilize the added resources available in the PS4 Pro, Sony is working on a firmware upgrade

Source: Hot Hardware – PS4 Pro Boost Mode Nets Up To 38 Percent Performance Boost For Some Games