Both the Galaxy Note 3 and Galaxy Note 4 are getting an update on two different carriers in the U.S. The bigger update is for the Galaxy Note 3 on Verizon, which brings the device to Android version 4.4.4. The update has build number N900VVRUDNJ6 and packs a number of features in addition to the security and bug fixes of Android 4.4.4. These include improved LTE connectivity and voice reception, KNOX version 2.0, Kids Mode, and bug fixes for VPN, SMS and Bluetooth audio.
As for AT&T's Galaxy Note 4, the update's most significant feature is support for HD VoiceSM for improved sound quality in voice calls. The update also brings a couple of applications to add to the existing bloatware, including Amazon Shopping, Evernote, and Softcard. Both the Verizon and AT&T updates are making their way over-the-air, and owners of the Note 3 and Note 4 should be getting notifications in the next few days.
Update: Verizon is pushing a new update to the Galaxy Note 3. The new OTA is based on Android 4.4.4 as well but has a new build number (N900VVRUDNK1). It seems to have no new features or changes, suggesting this could be a minor update to fix any issues folks might have had updating to the original 4.4.4 update.