Last month it was reported, including by Microsoft, that the upgrade from 24H2 to 25H2 would be accomplished with a tiny [<1MB] update. It's still not available on the update catalog site, and it hasn't shown up in Windows Update on our Win11 hardware compatible PCs. Today the an update, KB5067115, was released for both the Insider Beta & Dev channels, bringing them both to the same 25H2 build, 26220.7051. When it installed on my copy of Win11 24H2 enrolled in the Insider Beta channel it performed a complete reinstallation. That does Not mean that's what will happen with every non-Insider copy of WIn11 24H2, but it does not rule it out either. Microsoft may have had their reasons for performing a complete reinstall, or they could have screwed up [as they often do], or the may have changed their mind on using a small, simple enablement update.