Sideloading Change in Windows 8.1 Update 1

Q: What is the sideloading change in Windows 8.1 Update 1?

A: Windows 8.1 Update 1 Professional installations that are joined to a domain now don't require a sideloading key to sideload "modern" applications (which means they behave the same as Windows 8.1 Enterprise installations). Additionally, sideloading keys are now included with several types of Microsoft agreements, and a $100 sideloading key is available that covers an unlimited number of devices. Details can be found at the MSDN blog site.