Windows 9, the never-launched operating system that was supposed to hit the market before Windows 10, is mentioned once again in a recent patent filed by Microsoft and published on March 31.

Microsoft has never revealed the reason it never launched Windows 9 and instead preferred to skip from Windows 8.1 to Windows 10 (aside from the fact that the differences between the old and the new release were so big that an important version jump was necessary), so it’s interesting to see it mentioned in new documentation.
Spotted by @h0x0d (via NPU), the patent brings forward a new theory: Windows 9 was supposed to be the version launched last year while the Redstone update coming in July was originally projected to be called Windows 10. Of course, this is just speculation and nothing is certain, but it appears that Threshold was original supposed to be Windows 9, and that’s why it shows up in various references every once in a while.
The Windows 9 secrecy Here’s an excerpt from the patent where Windows 9 is mentioned, but this doesn’t provide any kind of information regarding its release date or why it was replaced with Windows 10:
“Some discussion herein is derived from some Windows 9 ‘Threshold’ documentation. Windows 9 is software implemented by Microsoft Corporation, and along ‘Threshold’ refers generally in marketing or other materials (from third parties as well as Microsoft) to a version of the Microsoft Windows software (marks of Microsoft Corporation).”
Without a doubt, Microsoft will never provide any other information on Windows 9, so it’s very clear that this version is nothing but history. And since the company is already working on future updates for Windows 10, it’s very clear that Redmond is less interested in discussing past plans these days.
So for the moment, the only good reason Windows 9 never came to be is still because 7 8 9.