A back panel of the supposed iPhone 5S has been leaked online suggesting internal changes. See also: Live coverage of Apple 2013 iPhone event from Cupertino, California.
The iPhone 5S is tipped to be Apple's next smartphone and the rear casing may have been leaked online. The image, picked up by Apple Insider, shows a different design with screws in an alternative arrangement to the current iPhone 5. See also: iPhone 5S release date. See also: iPhone 5S price in the UK.
The part claims to be from the upcoming iPhone 5S. However, is possible that it is an unused prototype design of the iPhone 5.
It is likely that the iPhone 5S, if that's what Apple calls it, will have a similar design to the iPhone 5 but with internal changes. After all that’s what happened between the iPhone 4 and iPhone 4S and iPad 3 and iPad 4.
Unfortunately the different configuration of the case gives no indication as to what the changes might be. (See also: iPhone 5C vs iPhone 5S comparison review: what's the difference between iPhone 5C and iPhone 5S?)