diff --git a/cylc/flow/__init__.py b/cylc/flow/__init__.py
index f512055d8d..6e9d18ee57 100644
--- a/cylc/flow/__init__.py
+++ b/cylc/flow/__init__.py
@@ -53,7 +53,7 @@ def environ_init():
 
 environ_init()
 
-__version__ = '8.6.3'
+__version__ = '8.6.4.dev'
 
 
 def iter_entry_points(entry_point_name):