According to Win8China, Internet Explorer 11 is currently in development and will be included in the next major update to Windows named "Windows 8.1" (aka 'Blue') that is expected to be released this summer.
The F12 developer tools screenshot above shows "Browser Mode: IE11". I didn't notice any visual changes at this stage, but it leads us to believe that IE11 will ship with Windows 8.1.
As we wrote earlier, according to the rumor, the major update will also bump the kernel version to 6.3. Leaked screenshots confirm this rumor.
It looks like Windows 8.1 will be a major update.