According to the new leak, the Taiwanese manufacturer's phablet contender will run Android 4.3 Jelly Bean with its custom Sense 5.5 UI on top...
Source: http://www.phonearena.com/news/HTC-One-Max-phablet-to-come-with-Sense-5.5-slapped-over-Android-4.3-UltraPixel-camera-and-LTE-support_id46806
Source: http://www.phonearena.com/news/HTC-One-Max-phablet-to-come-with-Sense-5.5-slapped-over-Android-4.3-UltraPixel-camera-and-LTE-support_id46806