Just to confirm i face similar problem. Yes i saw that warning too : "Upgrade Cluster Compatibility Level" to upgrade the Cluster to version 4.5. Though when i try to do that there are a lot of errors. In GUI : Error while executing action: Cannot change Cluster Compatibility Version to higher version when there are active Hosts with lower version. -Please move Host host1, host2, host3 with lower version to maintenance first. In engine.log : WARN [org.ovirt.engine.core.bll.UpdateClusterCommand] (default task-163) [2c681b74-8666-4f2f-b2e0-6b20e98f417e] Validation of action 'UpdateCluster' failed for user admin@internal-authz. Reasons: VAR__TYPE__CLUSTER,VAR__ACTION__UPDATE,$host host1, host2, host3,CLUSTER_CANNOT_UPDATE_COMPATIBILITY_VERSION_WITH_LOWER_HOSTS I did not find any documentation for 4.5 cluster compatibility, so i like as well to understand why is that option present there. It will be used when ovirt 4.5.x will be released ?