https://wccftech.com/ratchet-clank-rift-apart-performance-rt-mode-was-a-last-minute-discovery/

The Ratchet & Clank: Rift Apart Performance RT mode that has been added to the game with the day one patch was a last-minute discovery, according to Insomniac's Director of Core Technology.

Speaking with Axios, Mike Fitzgerald confirmed that the game was supposed to launch with only Fidelity and regular Performance mode, but, towards the end of development, the studio discovered, thanks to the different teams working together, that more performance could be squeezed out of the PlayStation 5.