It's still Trident, though
The ever reliable Mary Jo Foley of All About Microsoft on ZDNet is reporting that, despite expectations that Microsoft is working on developing Internet Explorer 12, Microsoft is in fact working on an entirely new web browser developed from the ground up using the existing Trident core. The new web browser, which is expected to ship alongside Windows 10 and is codenamed Spartan, sticking with Microsoft’s Halo inspired codenames for the next version of Windows, will feature versions both native to the “Modern” tablet experience as well as the desktop.
Microsoft will reportedly ship Windows 10 with both the new Spartan web browser alongside the existing version of Internet Explorer 11 found on Windows 8.1 devices for backwards compatibility purposes. According to Jo’s sources, “Spartan” will feature a brand new, streamlined, user experience that more closely resembles other modern web browsers, including Google’s Chrome and newer versions of Mozilla Firefox.
Microsoft may not be on track to ship a beta version of “Spartan” in time for the official Windows 10 Consumer Preview in January, however it will likely ship with a future build pushed to Windows Insiders not long after.
Source: All About Microsoft