ArcGIS Enterprise to ArcGIS Enterprise collaboration
ArcGIS Enterprise collaboration participants may include versions 10.5.1 and 10.5. Keep in mind that any participants using version 10.5 will only have capabilities available for that version. For example, hosted feature layers may be shared by reference only.
ArcGIS Enterpriseand ArcGIS Online collaboration
The minimum version for ArcGIS Enterprise to participate in collaboration with ArcGIS Online is 10.5.1.