If you've got a Samsung phone from before the Note 3 and you're on an American carrier, you're probably wondering where your Android 4.3 update is already. The leaked schedule below has been verified to Android Police by two reliable sources, and shows when the 4.3 update is scheduled for the Galaxy S III, Galaxy S4, Galaxy S4 Active, and Galaxy Note II on AT&T, Verizon, Sprint, and T-Mobile. This update will also add support for the Galaxy Gear to these devices.
As you can see, almost everyone should have a 4.3 update ready by the end of November, with T-Mobile's Note II stretching into early December and AT&T's exclusive Galaxy S4 Active waiting until almost Christmas. Even so, the release schedule is surprisingly accelerated by American standards - it's probably got something to do with the fact that both Samsung and the carriers want to be able to sell the Galaxy Gear smartwatch to as many people as possible.
As noted in the leak, the dates above are subject to change. Given the general state of Android updates on AT&T, Verizon, Sprint, and T-Mobile, it's reasonable to assume that at least one or two of these will be delayed. Even so, it's an exciting roadmap of updates over the next couple of months. International versions of the Galaxy S4 Mini and Mega 6.3 will be updated to 4.3 eventually, but there's no word on their American counterparts yet.