A Reddit user says he inadvertently downloaded the promised OneDrive UWP app for Windows 10 from the Windows Store after sideloading the old Windows 8 version of the app.

OneDrive UWP

Reddit user "mcdenis" described what happened (via: Windows Clan):

The other day, I sideloaded the old OneDrive app for Windows 8 because it has a major advantage over the client that comes with Windows 10: it shows all my files, including those that are not synced locally. It also supports the share contract and it integrates fairly well in the file picker. This morning, I clicked on the OneDrive tile and guess what? The app that launched was actually the new UWP OneDrive app which is not even released yet on desktop PCs. To make sure I wasn't hallucinating or something, I reinstalled the old OneDrive app in another VM and right after that, the store started offering the new unreleased app as an update. I guess it won't be too long before it is released to insiders…

Microsoft previously confirmed it was working on a UWP OneDrive app for Windows 10 but did not give a release date. It's possible a preview version of the app will be released first to Windows Insider members before it is made generally available to all Windows 10 users.