While spelunking through the latest beta build of Windows 10, I was quite surprised to find that the Windows 7 and 8.1 interface for enabling the Windows Guest account is gone. Even in the legacy Control Panel's User Account applet, where turning on Guest was as easy as two clicks, there are no hooks for enabling the Guest account in build 10159.
That's surprising because there is full, traditional Guest account support in build 10130.
And in build 10159 it's possible to dig into Windows and turn on the Guest account. To do so through the Computer Management console using an admin account, right-click Start > Computer Management. Under System Tools > Local Users and Groups, click Users, then on the right, double-click Guest. Uncheck the box marked "Account is disabled" and reboot.
To enable Guest through the Group Policy Editor using an admin account, click on Cortana, type gpedit.msc and choose Microsoft Common Console Document. Navigate to Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options, then on the right, double-click Accounts: Guest account status and choose Enabled. Reboot.
But in my experiments, even after enabling it, there's no support for turning Guest on in the Control Panel Accounts applet, nor in the PC Settings app; and Guest doesn't appear on the sign-in screen.
A friend of mine reports that he was able to coax Windows into showing a Guest account, working through the Computer Management console, but when he clicked on the Dummies account on sign-in, Windows sent him to sign in with a different account. (t/h AR)
Microsoft has hidden Windows 10 features before, only to have them morph and reappear in odd ways -- Family Safety turned into the online Microsoft Safety; the old Photo Import feature suddenly appeared in the new Phone Companion app. But this one feels different. Even Cortana refuses to respond meaningfully to searches on "Guest account."
Bug? Feature? Hard to say.