How to find exact HTC One S version (S3/S4)
Easiest way. Check your packaging. Look for Model describtion on the back of the other label. Either z520 or z560, the z520 is S4, 560 is S3.

from wikipedia:

Processor and memory

One version of the One S uses a Qualcomm Snapdragon S4...In certain markets the One S uses the older Snapdragon S3... The two versions have slightly different packaging, the S4 is model Z520e/Z520m and states "Processor: Dual Core, 1.5GHz"/"CPU Speed 1.5 GHZ, dual core, whereas the S3 is model Z560e and states "Processor: Dual Core".