You likely know what the toggle switches look like on Windows Phone and in Windows 8.x – They are squared sliders, matching the Modern interface nicely. In Cortana on the latest Windows 10 Technical Preview, many people noticed that the service uses different toggles; ones which are rounded. Initially, I didn’t spot them anywhere else in the OS and wrote them off as a designer just trying something new, something that would go away in the next build.
For a comparison of the old style and the new style, below is a screenshot of the Settings app, which still uses the old style, and above are Cortana’s settings and the settings of the Xbox app as well.
Since this new toggle design has made an appearance in the Xbox app, I think it’s safe to assume that this design will migrate out to the rest of the OS, and on the phone side as well. It really makes sense, when you factor in the wireframe icon styling which is apparent here and there on both the phone and PC versions on the Windows 10 Preview.