The AT&T update is being rolled out over-the-air (OTA) and clocks in at about the same size as the Sprint update for the S4, but the update does not include the KNOX security suite. It does include the apps-to-SD feature and performance updates, but not KNOX.
The Verizon update is rolling out through Samsung Kies, not OTA, because that update is a massive 1.8GB. It seems that Verizon is pushing the full system image with the update included, rather than an incremental update like the other carriers. But, the update for Verizon does include the same changes as were found with the Sprint variant, including KNOX, apps-to-SD, performance updates and more.