http://techcrunch.com/2015/01/21/microsofts-browser-with-a-halo-codename/

“The new browser, which is unsurprisingly codenamed “Project Spartan,” will sadly not be in the next preview build of Windows 10 and it remains unclear when developers and users will get their hands on it. Microsoft also didn’t talk about any of the technical details of the new engine at its core”