Looks like Windows 8.1 Update 1 could come out next month as rumored. The guys at The Verge say they've been tipped off by "sources familiar with Microsoft's plans" that the software update has reached release-to-manufacturing status. Russian site WZor reports the same thing, adding that the RTM build was compiled on February 21 and signed on February 26.
If those sources are correct, then Windows 8.1 Update 1 is complete. The next step is to release it. According to Microsoft watcher Mary Jo Foley, that could happen on April 8, the day of next month's so-called "patch Tuesday."
As we've reported before, Windows 8.1 Update 1 is supposed to introduce a fair number of tweaks targeted at desktop users. Word has it non-tablet systems will boot straight to the desktop, for instance, and users will be able to bring up the taskbar inside of Modern UI apps. The Verge points out that the update is also expected to lower Windows' hardware requirements to 1GB of RAM and 16GB of storage space. Coupled with those rumored discounts for sub-$250 devices, that change might usher in cheaper Windows tablets.
The only thing we don't know is what Microsoft will call the update. Windows 8.1 Update 1 surely isn't the final name. According to The Verge, Microsoft labeled it a "spring" update last week, so perhaps that's a hint.