The first major difference is obviously the SoC. While the One M8 used
Qualcomm's
Snapdragon 801 with four Krait cores at 2.26GHz, the M8s opts for Qualcomm's Snapdragon 615 which has two clusters of four Cortex A53 cores at 1.7GHz and 1.0GHz respectively. It will be interesting to see how Snapdragon 615 compares to 801 with regards to performance as well as power consumption. On that note, the M8s is also able to fit a higher capacity battery in the same chassis as the original M8.
The last major difference between the two are the cameras. While the One M8 used HTC's 4MP "UltraPixel" sensor, the M8s opts for a 13MP sensor. Despite this, it retains the secondary depth camera which enables HTC's duocam post processing effects like depth of field and refocusing photos.
