Windows 10 is shaping up to be a big OS shift for many reasons, including the addition of a new web browser codenamed Spartan. Spartan is still very experimental and as such, it is not included in the current Preview for Windows 10. However, bits of the rendering engine can be engaged in the older Internet Explorer 11.
AnandTech forced the new Edge document mode in IE11 through a simple trick using about:flags. They then compared the new rendering engine to legacy IE11, Chrome 40, and Firefox 35. The results are very impressive so far, demonstrating that even in these early stages, what powers Spartan could be quite powerful.
AnandTech says the following about the changes so far:
There are still many months before we see Spartan under ideal conditions and a more finalized form, but so far, Microsoft appears to be nailing a lot of the performance issues. Even better, since Spartan is a Universal app, it gets updates through the Store instead of OS refreshes. This change means Microsoft can dynamically update and tweak the browser at a much faster clip than in the past.
Head to AnandTech to read the full write-up including more technical details about Spartan!