Anandtech published Windows 10 Build 10049: Meet Project Spartan
A quote from the article:
Microsoft has released a new build to the fast ring for Windows Insiders today. When build 10041 dropped on the 18th of March, we made note that updates would not be coming at a much quicker pace. Little did we know that we would get a new build only twelve days later. There is big news with this build as well with the public availability of Microsoft's new browser, codenamed Project Spartan.Windows 10 Build 10049: Meet Project Spartan @ Anandtech
Back in January we took a look at some of the parts of Project Spartan. At that time, the goal from Microsoft was to include the new rendering engine which would be the heart of Spartan in both Internet Explorer and the new, as yet unnamed browser. Those plans have shifted though. Internet Explorer will still be available for legacy applications (think business) but it will not include the new rendering engine, which is EdgeHTML. Project Spartan will be exclusively EdgeHTML and not include the legacy MSHTML rendering engine for compatibility. Microsoft's metrics on compatibility with the new browser have shown them that it is really not necessary. So the new browser should be free of any of the legacy code which caused issues with standards.