Somewhat confusing. Does not mention if browser will automatically convert to IE11 if page does not render (doubtful). I still have problems on some sites not properly rendering with IE11. Part of lengthy article:

The existing version of Internet Explorer will ship in Windows 10 alongside Microsoft’s new Spartan browser, the company revealed Thursday. This is instead of a new version of IE, which was being referred to as IE12 by Microsoft officials as late as Wednesday.
In an effort to clarity issues raised during Microsoft’s Windows 10 preview event,”>the company posted a blog entry Thursday saying the new OS will ship with a new, minimalist browser code-named Project Spartan. The blog post also revealed that IE will also be in the new OS, but referred not to a future IE12 but instead to the current IE11.
Group Program Manager Jason Weber said in the post that the inclusion of IE is necessary for displaying Web sites that use older Microsoft technologies, such as ActiveX. Including the existing rendering engine, known as Trident, as a fallback for Spartan will allow websites that may not have adopted HTML5 standards to continue to be rendered as their developers intended.

Spartan and IE11 to coexist in Windows 10 | PCWorld