From https://grapheneos.org/faq#recommended-devices :
8th generation and later Pixels also have support for the incredibly powerful hardware memory tagging security feature as part of moving to new ARMv9 CPU cores. GrapheneOS uses hardware memory tagging by default to protect the base OS and known compatible user installed apps against exploitation, with the option to use it for all apps and opt-out on a case-by-case basis for the few incompatible with it. Pointer authentication, branch target identification and other ARM security features were also introduced at the same time as hardware memory tagging.