Hello - Esri support sent me a notification for an ArcServer 10.9 patch 7918 at http://support.esri.com/en/download/7918
From the support download page, for Enterprise>ArcGIS Server> ArcGIS Server> 10.9 the patch reads "ArcGIS Server 10.8.1 Utility Network Patch 4". The patch also does not yet appear in the Patch Notification tool for ArcGIS Server 10.9
Thanks
