The first country to get the update is Germany, but other regions will supposedly be joining the whitelist shortly. German Samsung Galaxy S4 users can update both OTA or via the Samsung Kies computer software.
The Android 4.3 update brings quite a few new features, although most of them are part of Samsung's proprietary TouchWiz UI launcher and not the OS itself.
Here is the complete changelog for the update as compiled with SamMobile:
- OpenGL 3.0 Support
- GALAXY GEAR Support
- TRIM Support (Makes the device much faster)
- ANT+ Support vSamsung 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)
Currently the Android 4.3 update is available only for the I9505 Galaxy S4 LTE-enabled model running on Snapdragon 600. SamMobile claims the octa-core I9500 will follow suit next week, the Galaxy S III will be getting its 4.3 release next month, while the Galaxy Note II will get the Android 4.3 treatment in December.
The reason why the former Samsung phablet is taking so long to reach Android 4.3 is the huge number of S Pen-related features that need to be ported to the lasest Android release.