In a Gamescom virtual event relatively light on content, the release of a free 60 frames per second PS5 upgrade for Horizon Zero Dawn was a definite highlight, giving another Sony first-party classic the full frame-rate upgrade and dramatically improving the experience as a result. This patch is an interesting, because unlocking 60fps is not as easy as flicking a switch, as demonstrated by the initial release of the PC version last year. This showed that simply removing the frame-rate cap brought into a focus a range of issues for a game designed primarily with 30fps in mind. Put simply, it's clear that this patch took real effort to produce and it's likely that many of the solutions in the revised PC version worked their way back to this new PlayStation 5 upgrade too. The bottom line is that however Guerrilla managed it, it works, and it works well.
So, what does the patch actually do? On the face of it, Horizon Zero Dawn follows the template laid down by the God of War, Days Gone and the initial Ghost of Tsushima patches in that graphics are totally unchanged from the original release and frame-rate is unlocked, with v-sync providing a 60fps limit. That means that the 2160p checkerboarding solution remains in place, but the PS4 Pro's alternative 1368p native rendering performance mode option has been removed as it's essentially redundant. Despite no improvements in how the game renders, there's an argument to say that graphics have improved perceptually thanks to the frame-rate upgrade - simply because checkerboarding artefacts persist for just one display refresh now rather than two. On a modern LCD screen, this helps to blend them somewhat, making them less noticeable.
In terms of actual performance, you are effectively looking at a locked 60fps experience that is nigh-on perfect. Even in backwards compatibility mode, PS5 offers substantial upgrades over PS4 Pro - a 2.5x multiplier in compute performance and twice the memory bandwidth. In prior 'back-compat plus' first-party patches, we've seen that translate into a performance bump that scales almost in line with the compute boost. With Horizon Zero Dawn specifically, we only noted one slight drop in an early cutscene, then it was a straight 60fps from there on out. If the game does deviate from the 60fps target, it should only do so fleetingly and you may not notice it at all. I'd describe performance overall as impeccable.