HTC One M9 has 5in screen with a Full HD resolution of 1920 x 1080 and a pixel density of 441 per inch. It is powered by a 64-bit, octa-core Snapdragon 810 processor and 3GB of RAM. HTC has replaced the Ultrapixel rear camera with a 20MP one, while the front camera is a 4MP Ultra Pixel sensor, letting a claimed 300% more light into your selfies than the M8 managed. The internal storage is 32GB with a microSD card slot worth up to 128GB.
HTC One M9 is yet to receive official Marshmallow update in all the regions. If you are tired of waiting for the official update, you can always use custom ROMs. CM 13 ROM will update One M9 to Android 6.0 Marshmallow. A detailed guide on how to install CM 13 on HTC One M9 is given below.