Microsoft requires migration to Windows 8.1 Update within 5 weeks
Source
A Guy
Microsoft yesterday confirmed that Windows 8.1 users must upgrade to Windows 8.1 Update, the refresh that begins rolling out to customers today.
"Failure to install this Update will prevent Windows Update from patching your system with any future updates starting with updates released in May 2014," said Michael Hildebrand of Microsoft in a Monday blog.
Source
A Guy