According to BuildFeed, Microsoft has compiled a build of Windows 10 that's made for foldable devices. It's from the 19H1 development branch, and the build number is 18313. That's about all we know.
Beta Channel preview adds OneDrive alerts, fixes high CPU usage, and more
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Build 25252.1010 (KB5021855)
Latest Windows 11 Dev Channel Preview is a servicing pipeline update