We knew it wouldn't be long, and sure enough, the Android 4.3 update has started hitting Google Play Edition devices. Both the HTC One and the Samsung Galaxy S4 from Google Play are currently receiving update notifications. If you're lucky enough to have one of these devices, commence mashing the update button at your leisure.
The updates for both devices are developed by the OEMs, but there are no modifications to the UI and no carrier testing to get in the way. As a result, we get this super-fast update. The HTC One kernel and framework source just dropped today, in fact. Hopefully all future updates come out this fast. The Nexus phones only started seeing Android 4.3 in the last week or so, and some users haven't gotten the notification yet.
The HTC One update clocks in at 185MB and the Galaxy S4 is a comparatively slim 150MB. We've got a mirror of the HTC One update below, but haven't seen the GS4 pop up anywhere. There are no official full factory images for these devices yet. Google clarified prior to release that the OEMs would be responsible for posting such images, if they cared to. It appears they do not, at least not yet. Also of note, the update enabled the One's IR blaster. Bluetooth tethering has been added to the GS4, but no word on IR yet.