Thanks for your response.
Yes, Azure does upgrade the underlying OS with security patches automatically. However, some upgrades do require reboots which they don’t do. Therefore, it is an excellent strategy to timely reboot your OS. Check out https://docs.microsoft.com/en-us/azure/aks/node-updates-kured for more info on how to automate it.
If your question is regarding auto-updating, the kubernetes version in AKS “Cluster Auto Upgrade” feature is under development.
However, doing a manual upgrade is just a few commands away:
Check out https://docs.microsoft.com/en-us/azure/aks/upgrade-cluster#upgrade-an-aks-cluster for upgrading your cluster to the latest k8s version.