This version will be on CRAN once some backwards dependencies have been updated. It would be really wonderful in the mean time if this was available on Conda as well.
I am the maintainer of the other Stan backend, CmdStan, on Conda, but I am not very familiar with the R environment or how possible this will be.
The Stan Development team has released a version of RStan/StanHeaders which supports Stan 2.26, available here: https://github.com/stan-dev/r-packages. More information here: https://mc-stan.org/r-packages/
This version will be on CRAN once some backwards dependencies have been updated. It would be really wonderful in the mean time if this was available on Conda as well.
I am the maintainer of the other Stan backend, CmdStan, on Conda, but I am not very familiar with the R environment or how possible this will be.