diff --git a/mitmproxy/version.py b/mitmproxy/version.py
index a047d86f6..b87cabc79 100644
--- a/mitmproxy/version.py
+++ b/mitmproxy/version.py
@@ -2,7 +2,7 @@ import os
 import subprocess
 import sys
 
-VERSION = "8.1.1"
+VERSION = "9.0.0.dev"
 MITMPROXY = "mitmproxy " + VERSION
 
 # Serialization format version. This is displayed nowhere, it just needs to be incremented by one