Microsoft makes Spartan the default browser in Windows 10
Windows 10 build 10049 was the first to come with a testing version of Spartan browser, the new app supposed to replace Internet Explorer, while build 10051 brought a few new things to the table to make it more stable and reliable in the technical preview.
In both builds, however, Internet Explorer was still the default browser, so even if you were using Spartan as your main driver and were clicking a link in a different app, IE was the one to load it.
Starting with build 10056, Spartan officially becomes the default browser in Windows 10, so Internet Explorer is slowly fading out and becoming the second option for users running the new operating system.