diff --git a/doc/manual/rl-next/nixversion-fake.md b/doc/manual/rl-next/nixversion-fake.md
new file mode 100644
index 000000000..1a97e412c
--- /dev/null
+++ b/doc/manual/rl-next/nixversion-fake.md
@@ -0,0 +1,11 @@
+---
+synopsis: "`builtins.nixVersion` now returns a fixed value \"2.18.3-lix\""
+# prs: cl 558
+---
+
+`builtins.nixVersion` now returns a fixed value `"2.18.3-lix"`. This prevents
+feature detection assuming that features that exist in Nix post-Lix-branch-off
+might exist, even though the Lix version is greater than the Nix version.
+
+In the future, check for builtins for feature detection. If a feature cannot be
+detected by *those* means, please file a Lix bug.