Each minor version of ARMv8 has a lot of optional extensions. What ARMv9 does is make some of those features mandatory. ARMv9 also includes new optional feature

Each minor version of ARMv8 has a lot of optional extensions. What ARMv9 does is make some of those features mandatory. ARMv9 also includes new optional features such as Scalable Vector Extensions 2 (SVE2) and Confidential Compute Architecture (CCA) (Intel SGX / AMD SEV equivalent).