diff --git a/optuna_integration/version.py b/optuna_integration/version.py
index 4acdd9b1..65ac68de 100644
--- a/optuna_integration/version.py
+++ b/optuna_integration/version.py
@@ -1 +1 @@
-__version__ = "4.0.0.dev"
+__version__ = "4.0.0b0"