Microsoft promised that Windows 10 builds would be coming more often, and it looks like that's happening. It's not even two weeks since the last build, and another build—number 10049—is out today. Fast track users should find the build available immediately.

The big change in this version: it includes Microsoft's new, legacy-free browser, codenamed Project Spartan. This is the first public outing for the new browser, with its reduced, Chrome-like interface and Cortana integration.

This first iteration isn't feature complete, as major pieces such as history and downloads are not available yet. However, the big new features that Spartan brings—annotations and notes on Web content, reading mode, and, of course, Cortana—are all available, to a greater or lesser extent. In common with earlier Cortana previews that were geographically limited, Spartan's Cortana will initially only work in the US. Announcing the new build, Microsoft's Joe Belfiore emphasized that this is "NOT a polished, ready-for-everyone release," and that it will be held for the addition of features and improvements before it's made broadly available. Likewise, known issues with the Windows build itself mean that some may want to stick to the slow track for the time being.

Spartan will be the default browser in Windows 10. Accordingly, Spartan, and only Spartan, will be pinned by default to the Start screen and taskbar. Internet Explorer 11 will still be available, but you'll have to search for it to get it.

The new build should incorporate changes in the browser's rendering engine that Microsoft announced last week. The company's initial plan for Windows 10 was for Project Spartan to be able to switch to the legacy Internet Explorer "Trident" rendering engine when necessary, and similarly, for Internet Explorer to be able to use the new Spartan "Edge" rendering engine when appropriate.

The new plan is for Project Spartan to only offer the Edge engine and for Internet Explorer to only ever use the Trident engine. In many ways this makes the difference between the browsers more clearcut—Internet Explorer is solely the legacy browser, used only when its compatibility with old sites and old extensibility mechanisms (browser toolbars and ActiveX extensions) is necessary, while Project Spartan is the regular day-to-day browser that forfeits compatibility with all of those.

As a result, enterprises that need the legacy compatibility of Internet Explorer, but also want the modern engine of Spartan for regular browsing, will be forced to use both interfaces and also use Microsoft's admin tools to make sure that Internet Explorer is automatically used for those legacy URLs.