No patching needed for apparent improved performance on some legacy titles.

https://youtu.be/fqu1ObkxBAs

Thus far, to get a benefit from the extra hardware inside the PS4 Pro, developers have had to code game-specific patches to activate features like higher resolutions, smoother frame rates, or increased detail on in-game objects. Now, there are signs Sony is planning to add an optional "Boost Mode" that could smooth out the frame rate on some older titles without the need for any specially coded patches.

While the Boost Mode was not mentioned in today's official announcement of the coming Version 4.5 of the PS4 firmware (which also adds external hard drive support), reports of its existence are starting to leak out from users who are signed up for the beta version, which launched today. In a NeoGAF thread, a few posters have uploaded separate screenshots, apparently from the beta, describing the Boost Mode in both Japanese and English.

The English description for the mode reads:

Experience improved gameplay, including higher frame rates, for some games that were released before the introduction of PS4 Pro (CUH-7000 series). Turn this off if you experience unexpected behaviour during gameplay.

Some beta participants are also posting videos apparently showing how that improvement looks in action. This comparison shows Boost Mode reducing extremely prevalent frame rate stuttering in the PS4 version of The Evil Within. Another video shows what's purported to be improved frame rate on Just Cause 3 through the use of PS4 Pro's Boost Mode.

As far as we can tell, Boost Mode seems to work by simply taking out the stops that Sony itself put on the PS4 Pro to ensure compatibility with games coded for legacy PS4 hardware. As Sony's Mark Cerny explained to Eurogamer back when the PS4 Pro launched in October:

First, we doubled the GPU size [for the PS4 Pro] by essentially placing it next to a mirrored version of itself, sort of like the wings of a butterfly. That gives us an extremely clean way to support the existing 700 titles. We just turn off half the GPU and run it at something quite close to the original GPU... For variable frame-rate games, we were looking to boost the frame-rate. But we also wanted interoperability. We want the 700 existing titles to work flawlessly.

Even for games that don't encounter the menu's suggested "unexpected behavior" when suddenly running on a GPU with more compute units and clock speed, Boost Mode may not lead to any noticeable performance improvement. If a game was coded with a frame rate that was explicitly "locked" to certain timestamps, for instance, Boost Mode can't improve on that without a specific patch for the game.

The idea of an unlocked hardware mode for older PS4 titles on the PS4 Pro isn't an entirely new one: Digital Foundry, for one, suggested back in August that the PS4 Pro could offer a mode that "was enhanced with the faster CPU and GPU resources available with the new hardware." While Sony has yet to confirm any of this, all signs point to the company finally taking that advice.