Thanks everyone! For anyone who wants to try out the release candidate with CmdStanR you can install it easily using
rc_2_24 <- "https://github.com/stan-dev/cmdstan/releases/download/v2.24.0-rc1/cmdstan-2.24.0-rc1.tar.gz"
cmdstanr::install_cmdstan(release_url = rc_2_24, cores = 4)
You may need to manually set the path the next time you use CmdStanR using
# replace with your path
set_cmdstan_path("/Users/jgabry/.cmdstanr/cmdstan-2.24.0-rc1/")
because I think we have it default to the latest installed release (not release candidate).