The good folks over at SamMobile have snapped up a pre-release copy of Android 4.3 for the Samsung Galaxy S4 (GT-I9505). If you are adventurous and want to flash the new firmware, just be aware that this is a test version, but SamMobile reports that it is stable.
They also say that the performance has been enhanced, being faster with less lag. Most of the improvements are behind the scenes, but a few tweaks that you will notice is a new and improved keyboard, a new Reading Mode that optimises the screen for reading, and improved colour reproduction for the display, making everything look sharper.
Samsung Wallet and Samsung Knox are included, with Knox working well, but Wallet not available yet. Samsung Knox separates your personal from work information on the one handset, which would be a boon for security conscious business users.
Remember that this is a test version and is still under development, so Samsung may yet add more features before the final roll out. The official version of Android 4.3 for the Galaxy S4 (GT-I9505) is expected to be sent to non-carrier bought phones in late October/early November.
Here is the Android 4.3 download with instructions, courtesy of SamMobile.