Well, after a fashion. Mary Jo Foley, the Microsoft Lady, (as I think of her) writes that Windows 10 may ship with both Internet Explorer and a new, lightweight browser (codenamed "Spartan") that looks a bit more like Chrome or Firefox. She also recalls mention of a possible rebranding of IE to try and escape some of the bad press it has gotten over the years - some deserved, some not. Currently, the Preview Builds on Windows 10 have Internet Explorer as one would expect.
However, if my sources are right, Spartan is not IE 12. Instead, Spartan is a new, light-weight browser Microsoft is building.
Windows 10 (at least the desktop version) will ship with both Spartan and IE 11, my sources say. IE 11 will be there for backward-compatibility's sake. Spartan will be available for both desktop and mobile (phone/tablet) versions of Windows 10, sources say.
Spartan is just a codename at this point. My sources don't know what Microsoft plans to call this new browser when it debuts. The IE team hinted during a Reddit Ask Me Anything earlier this year that the team had contemplated changing the name of IE to try to get users to realize the much more standards-compliant IE of today is very different from older, proprietary versions of IE.ZDNET