My HTC One (M7) received its OTA update from Android 4.4.2 (KitKat) to Android 4.4.3 (KitKat) yesterday (24 August 2014).
It seems that this update focuses on security fixes, particularly the fix for OpenSSL vulnerabilities (Heartbleed Bug and some other bugs).
Visually, there is no noticeable change from the previous version. The Software Information section in the phone informs us that:
- Android version updated from 4.4.2 to 4.4.3
- HTC Sense version updated from 5.5 to 6.0
- Software number updated from 4.20.707.6 to 6.13.707.1
- HTC SDK API level updated from 5.69 to 6.25
- Kernel version remains as 3.4.10