As of tomorrow, April 8, all Windows 8.1 users will be able to move to Windows 8.1 Update.
Microsoft will be making the Update -- formerly known by those of us who've been tracking it for a while now as "Update 1" and/or "Spring Update" -- available via Windows Update. This just in: It will be available starting around 10 a.m. PDT/1 p.m. EDT Tuesday via the Control Panel, meaning users can manually obtain and install it. Automatic delivery of the Update will be throttled, so users may not see it show up until some time later.
The Update, designed primarily to make Windows 8 more palatable for mouse/keyboard users, will be designated as an "Important" security update when it's rolled out tomorrow. It's actually very important, as Microsoft is going to require all Windows 8.1 users to have Windows 8.1 Update installed if they plan to continue to download any security or feature updates to the operating system.
Microsoft's Premier Field Engineering blog, in an April 7 post outlining the update, makes this plain:
The Windows 8.1 Update is cumulative and includes all previously released security and non-security updates. It also requires users be running Windows 8.1 as a prerequisite, so those still running plain-old Windows 8 need to do a two-step upgrade, the Premier Field Engineering folks note. Update: Those running Windows 8 will be able to move to 8.1 Update without updating to 8.1 first, Microsoft officials said.
As the Ask Premier Field Engineering blog notes, Windows 8.1 Update "will likely change your system's current behavior." Those using devices other than pure touch tablets will see their systems boot to Desktop by default, though users can change this setting and still boot straight to the Metro-Style/Start Menu if they prefer.
The Start Menu and windowed Metro-Style apps that Microsoft officials acknowledged were coming are NOT part of this Update.
The Windows Server version of the update includes all the previously-released monthly roll-ups, updates and security fixes since RTM; various bug fixes; Enterprise Mode for Internet Explorer (also included in Windows 8.1 Update) and more.