On Christmas day, an internal build of Windows 10 (version 14997) leaked to the internet. Unlike the Preview builds that Microsoft distributes to Windows Insiders, which are mostly-complete builds intended for QA testing, this leaked build appears to include early versions of multiple unannounced features. According to Twitter user WalkingCat (@h0x0d), the 14997 build includes a new "Game Mode."
.@h0x0d looks like Windows will adjust its resource allocation logic (for CPU/Gfx etc.) to prioritize the "Game" when running in "Game Mode"
— WalkingCat (@h0x0d) December 28, 2016
WalkingCat is the same person who first broke the story that Microsoft could be working on a hybrid emulation scheme for x86-on-ARM64. This time around, the Windows hacker-at-large seems to think that Game Mode might bring a console-like low-overhead gaming experience to desktop Windows by adjusting the balance of hardware resources to favor running games.
The idea isn't exactly far-fetched given that the Xbox One already does something similar to Game Mode, and (at least in theory) that machine runs on a good part of the same codebase as desktop Windows 10. Sadly, there isn't a lot of detailed information about the purported Game Mode. It's not clear whether the new mode would be available strictly for Windows Store apps, or whether it would apply to standalone games and those purchased through Steam, GoG, and other services.
Windows 10 Build 14997 includes some other new stuff besides Game Mode. A new Cortana-focused setup program allows users to install the OS using voice commands. Themes can be applied in the Settings app, rather than requiring users to open the old Personalization applet. There's also an automatic blue light-reduction feature that can be configured to adjust the display's color temperature based on the time of day. All of these features and more should be coming in the Windows 10 Creators Update, expected to launch early next year.