Gabe Aul, the head of Microsoft's Windows Insider program, in a blog post today announced that Microsoft has rolled out it’s first Windows Insiders Preview build after RTM having build no. 10525. If you are a Windows Insider in the first ring, check for Windows Update and you might have receive it by now.
Remember that, it’s a preview build and has numerous known issues. These issues are already published by Microsoft and mentioned in this post too.