Thanks to an insider ninja, Sammobile.com was able to obtain an Android 4.3 Jelly Bean firmware destined for the Snapdragon 600-clad I9505 Galaxy S4. On a related note a very early Android 4.3 Jelly Bean build has been leaked for the Galaxy Note II as well.
The firmware for the Galaxy S4 and Note II are completely flashable through popular desktop app Odin with the one for the S4 built on September 20 with a European stamp on it. It brings a new Reading Mode, which eliminates unnecessary clutter from pages, a working Samsung Knox security app and more.
During today, we will provide the tutorials for installing new firmware. Also The software is expected to hit the device some time later this month.
As usual with these things, proceed with caution and only if you know what you are doing. These are both pre-release firmwares, but should not increase the binary counter or void your warranty, and so far the guys over at SamMobile.com seem happy about the stability of the package for the S4 while the firmware for the Galaxy Note II is still early and may have bugs throughout.