The Samsung Galaxy S4 LTE Edition (Model GT-I9505) already had a leaked version of Android 4.3 grace its silicon. Now the official version is hitting the airwaves. Samsung officially launched the newest version of Android for the this particular version of the SGS4. As of right now it is only hitting this device in Germany, although it should come to others eventually. It's unlikely we will see carrier versions of the SGS4 get the Android 4.3 anytime soon, but now that this is finished, it should start filtering out over the next couple of months. Here's a list of some of the updates found in the changelog:
Samsung Galaxy S 4 Android 4.3 Update Changelog
  • OpenGL 3.0 Support
  • GALAXY GEAR Support
  • TRIM Support (Makes the device much faster)
  • ANT+ Support
  • Samsung KNOX Implementation (KNOX bootloader and dedicated application)
  • Samsung Wallet comes pre-loaded
  • Improved RAM management
  • Improved Display colour reproduction (Display looks much sharper than before)
  • Improved TouchWiz Launcher (Much less launcher redraws and less lag)
  • New Samsung Keyboard
  • New Samsung Browser (Full screen by default, new tab interface and more)
  • New Reading Mode (Optimises display for reading, used by only a few specific applications)
  • New Camera firmware
  • Minor UI tweaks (Contacts app, Flashlight Widget, dialog boxes etc)

Source: SamMobile