When Windows 10 launches, it will do so with two Web browsers on board – IE11 (for backward compatibility), as well as a brand new one codenamed Spartan. This will be lightweight, will look a lot like Chrome or Firefox, and will support extensions.
Spartan isn’t IE12, but something completely new, as it turns out. It will be available for both the desktop version of Windows as well as the mobile one (for phones and tablets). As for the name – it apparently is just a codename. That said, it hasn’t yet been revealed what its commercial name will be.
The new browser may be showcased during Microsoft’s January 21 event, where we should get a lot more information about Windows 10. But that’s not a given, since it’s unclear whether Spartan will be functional enough by then to be included in the January Technical Preview build of Windows for computers, or for the mobile preview builds that should also surface early next year. So there’s still a possibility that it will get a later introduction.
Since Microsoft has been porting a lot of its core apps to iOS and Android recently, the same could happen to Spartan at some point in the future, the speculation goes. But because this isn’t even being rumored right now, you probably shouldn’t hold your breath.