Emacs' stan-mode : what happened to ac-stan?

I use emacs for a lot of my tasks, including (r)stan use. Whereas stan-mode and most of its companions are available on MELPA, ac-stan (enabling auto-complete mode for stan files) is not.

Furthermore, a cursory look at the Github repository leaves the impression that ac-stan has been informally deprecated : the configuration examples leave it disabled by default.

What is the future of this package ?

It seems you asked @kaz-yos on github (https://github.com/stan-dev/stan-mode/issues/63) and the short answer is that company-stan is the current autocompletion tool.