It seems the new preview version is part of an update that some Insiders are receiving. While it bumps the Windows 10 Calendar to version 16005.12130.40020, there is now also a toggle that asks users to “Try the preview”. If this toggle is selected an Insider will agree to have new features sent to them. These features may not be stable and will still be in development, including bugs. As is always the case, these unstable preview builds could render the Calendar app unusable if some bugs are bad enough. Still, some Insiders value this kind of early access to test tools before they go public. As always with the Insider model, in return for getting early features Microsoft is asking users to provide feedback to help stabilize those additions ahead of release. However, unlike some Insider services, this is a preview users can opt in and out of at will. Because of that toggle, users can turn off the preview ability whenever they want to. Of course, if the toggle is off early features will not longer be sent.
Calendar Update
As for the wider update, Microsoft says it has brought 34 new themes to the Windows 10 Calendar. Elsewhere, Version 16005.12130.40020 also improves the month view and simplifies the new event feature. Finally, Microsoft has also redesigned the account navigation UI. This is not the apparent overhaul of Calendar’s design. As we reported in September, leaked screenshots showed a cool new UI Microsoft has planned for the native Windows app. You can get the Mail and Calendar app from the Microsoft Store here.