Brave of them to do support for the vector extension, given that it hasn't been ratified / officially standardised yet[1]. It's still a work-in-progress. The final version of the vector extension may have small (or enormous!) incompatibilities, so you might be tied to one of their toolchains to use it properly, rather than something upstream.
1. https://github.com/riscv/riscv-v-spec/