Based on feedback from Windows Insiders, Microsoft has decided to release new Windows 10 Builds to Fast ring users often. Today they released the first update Build 10041 to Insiders on this accelerated cadence. Due to the change in cadence, this build does not yet include the Project Spartan preview yet. Microsoft also confirmed that it will be available in the next release.
But Windows 10 Build 10041 includes no.of new features and improvements to the rendering engine that will power Project Spartan. Read about it in detail here.