The ruggedized Galaxy S4 Active is real. It's been spotted on camera before, not to mention in various less dramatic leaks. The folks at MobileTechReview got their hands on one, and it looks pretty close to finished, assuming that they don't already have a production model. In the video below, you can see the tougher red chassis (probably water and dust-resistant to some degree) and physical navigation buttons, as previously featured on Samsung's Rugby models.
What's new in the video is confirmation about the guts of the S4 Active. While the Bosnian-localized unit makes it hard to verify, the narrator mentions a Snapdragon S4 Plus processor, notably less powerful than either the standard Exynos 5 octa-core or Snapdragon 600 featured on the standard Galaxy S4.