Pentax K-1 has a 36.0MP Full frame (35.9 x 24 mm ) sized CMOS sensor . You can shoot at maximum resolution of 7360 x 4912 pixels with aspect ratios of and 3:2. K-1 has a native ISO range of 100 - 204800 and it can save files in RAW format which gives you a wider room for post processing.
Pentax K-1 is not the highest resolution Full frame camera. Sony A7R V with its 61.0MP sensor is leading in this class. Check the comparison of Pentax K-1 vs Sony A7R V or take a look at Highest resolution DSLR cameras list.
Pentax K-1 DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. Pentax K-1 sensor has been tested by DxO Mark and got an overall score of 96 for its image quality. You can find the details of their analysis of Pentax K-1 here.
High Resolution Mode
Pentax K-1 has a special High Resolution mode where the camera takes multiple images of a scene while moving its sensor using the sensor shift image stabilization system and combine them automatically to create a much higher resolution image. This feature works best with static scenes and using a tripod is a must to minimize stitching artifacts.
Another important feature about Pentax K-1's sensor is the lack of anti-alias (Low-pass) filter. Removing anti-aliasing filter increases the sharpness and level of detail but on the other side it also increases the chance of moiré occurring in certain scenes. But wait! K-1 takes care of this problem for you. It has a unique and adjustable Anti-Aliasing Filter Simulator mode which can create the effects of a Low Pass filter electronically when you want to avoid moiré.
Let's look at how the size of the Pentax K-1's Full frame sensor compares with other standard sensor sizes.