diff --git a/README.md b/README.md
index b1b9d0a..c4405bf 100644
--- a/README.md
+++ b/README.md
@@ -42,6 +42,11 @@ source whynot-env/bin/activate
 pip install whynot
 ```
 
+WhyNot requires Python 3.12 or newer. On an older Python, `pip` skips the
+current release and falls back to WhyNot versions from 2020, which fail to
+build with an error about `sklearn` that does not mention the Python version.
+If you see that, check `python --version` first.
+
 You can also install WhyNot directly from source.
 ```
 git clone https://github.com/socialfoundations/whynot.git
diff --git a/docs/source/installation.rst b/docs/source/installation.rst
index add6615..ddc09dd 100644
--- a/docs/source/installation.rst
+++ b/docs/source/installation.rst
@@ -6,8 +6,15 @@ Installation
 Basic Installation Instructions
 -------------------------------
 
-WhyNot supports Python3 on both OS X and Linux systems. We recommend using `pip`
-for installation and isolating the installation inside a `virtualenv`_.
+WhyNot requires Python 3.12 or newer, on both OS X and Linux systems. We
+recommend using `pip` for installation and isolating the installation inside a
+`virtualenv`_.
+
+.. note::
+    On an older Python, ``pip`` skips the current release and falls back to
+    WhyNot versions from 2020, which fail to build with an error about
+    ``sklearn`` that does not mention the Python version. If you see that,
+    check ``python --version`` first.
 
 1. (Optionally) create a virtual environment.
 
diff --git a/whynot/simulators/opioid/.experiments.py.swo b/whynot/simulators/opioid/.experiments.py.swo
deleted file mode 100644
index 586fad6..0000000
Binary files a/whynot/simulators/opioid/.experiments.py.swo and /dev/null differ