In the recently released Windows 10 Build 10041, Microsoft didn’t include the upcoming Spartan web browser. However, an older Windows 10 build 10014 Wim file which includes Spartan web browser got leaked online. You can download and try it if you want. As it is an technical preview build, it is not stable as the latest build.
Also, Spartan build present in this leaked 10014 build is also not feature complete. It includes only basic features. Try at your own risk.
More details on build here.