diff --git a/CHANGES.rst b/CHANGES.rst
index bf4a7e17..e936a088 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -2,6 +2,12 @@
  Changes
 =========
 
+4.0.1 (unreleased)
+==================
+
+- Nothing changed yet.
+
+
 4.0.0 (2023-12-11)
 ==================
 
diff --git a/version.txt b/version.txt
index fcdb2e10..39c84160 100644
--- a/version.txt
+++ b/version.txt
@@ -1 +1 @@
-4.0.0
+4.0.1.dev0