Quite a lot of leaks from Sammy’s store are being uploaded online. Android 4.3 has already been leaked for the Galaxy S4 and Galaxy Note 2 earlier and now, Samsung Galaxy S3 falls in line. However, this update is only for AT&T Samsung Galaxy S3 I747, it can be downloaded and flashed to your device right now so you don’t need to wait for the official OTA update that should roll out on November 13 apparently according to a leaked document we earlier posted. The Android 4.3 update bring support for Galaxy Gear smart-watch but also bring KNOX issue to your device.
It is recommended that you flash the stock firmware to your device via Odin before you update it to Android 4.3. In case you have a rooted device, this update will revoke root access on the device and you may need to root it again. We also recommend you to backup everything you proceed using our data backup guide.
For people who would like to keep the KNOX status and SE Linux, you can go ahead with the Heimdall-flashable form of the ROM found in this thread.
If you have CWM on your device already, you can go ahead and download the Android 4.3 stock ROM zip file which isn’t rooted and KNOX enabled from here.
XDA Recognized Developer loserskater has repacked the update and posted a pre-rooted version of the ROM which doesn’t have KNOX and SELinux enabled. You can find it in this thread.