In addition to the way we normally upgrade Windows 11—downloading the full Windows 11 26H2 ISO, mounting it, and running Setup as an in-place upgrade—Microsoft now has a much faster method for PCs already running 24H2 or 25H2, with very little downtime. First install KB5124010, a large cumulative update of roughly 4–5 GB that places the common 26H2 system files onto the PC in advance; after installing it, the machine still shows 24H2 or 25H2 because the new version has not yet been enabled. Once KB5124010, or a later cumulative update, is installed, install KB5121794, which is a very small 26H2 enablement package that essentially acts as a switch to activate the 26H2 components already on the computer. After a normal reboot, the system becomes Windows 11 26H2. This is considerably faster than performing a full ISO-based in-place upgrade and involves very little downtime. This method works for Windows 11 24H2 and 25H2, but not 23H2, which must first be upgraded normally to at least 24H2.