A teaser image posted on HTC's Weibo page seems to indicate that it will be releasing an octa-core 64-bit processor smartphone at IFA on 4th September.
The phone in question is likely the HTC Desire 820, the successor to the Desire 815, which was first teased on another image posted on HTC's Weibo page, showing a timeline of HTC products, and ending with the 820:
Interestingly, Qualcomm has also posted this image on their Weibo page, showing an outline of a smartphone with a Qualcomm Snapdragon 615 processor inside it. Qualcomm's Snapdragon 615 utilizes 8 Cortex-A53 cores paired with an Adreno 405 GPU. The chipset is mainly designed for mid-range smartphones, which would fit the profile of the HTC Desire 820.