Currently a user upgrading from Cilium 1.7 to 1.8 will have to pass --set config.upgradeCompatibility=1.7 to keep upgrade compatibility [1].

Unfortunately that same user won't be able to upgrade to 1.9 without facing upgrade compatibility issues since we won't be able to distinguish the first version of Cilium that the user installed was 1.7 or 1.8 nor we will be able to distinguish if the user didn't want to keep upgrade compatibility. In case the user wants to use a new option introduced in 1.8 it is a problem if we want to detect which options should be kept with the default values or with breaking values to avoid compatibility issues.

[1] https://docs.cilium.io/en/latest/install/upgrade/#step-2-option-a-regenerate-deployment-files-with-upgrade-compatibility-recommended