The rstanarm package for version 2.12.1 was released this week and is now mirrored on CRAN. You can install it simply by executing in R
Little changed, although one serious bug was fixed: posterior_predict() would do the wrong thing following models estimated by stan_lmer or stan_glmer if the labels of the grouping factors contained spaces in them. Specifically, posterior_predict() would marginalize over those grouping factors rather than conditioning on them. This bug is likely about 6 months old, so if you have recently generated predictions from such a model with rstanarm, you should reestimate it using rstanarm 2.12.1.
Ben