I’m wondering if it might be prudent to backport any simple fixes to 2.19 (i.e., make a hotfix release). There were some fixes to some of the math functions, right?
Here’s my reasoning. It’s going to take several months before PyStan figures out a way to build non-header-only reliably. So lots of people are going to continue to use the 2.19 version of Stan.
Moreover, it might be many more months before we figure out a way to build on Windows specifically. (Figuring out a way to build Stan non-header-only on Linux is a different task than doing the same thing on Windows.)