The Google Pixel phone is the first to take use of the Qualcomm 821 chipset. This processor is 10% faster than the 820. It features Qualcomm's cutting-edge technologies. It was designed to support the current high-demanding apps, supports better connectivity and of course bumps up the graphics and photo processing capabilities of the device. It is also more power efficient, which translates to a longer battery life and has the processing power needed for mobile virtual reality, Google Daydream in our case.
For the camera, the Qualcomm 821 chipset features the 14-bit Qualcomm Spectra ISP, that supports photos at up to 28MP resolution with zero shutter lag. It supports X12 LTE which has three times the bandwidth of X10 LTE.
The chipset is the first to feature Qualcomm's custom-designed 64-bit quad-core CPU called Kyro. It supports Quick Charge 3.0 which can charge your battery up to 4 times faster than conventional charging, and that's why Google Pixel phone can charge your phone for 7 hours of use in as little as 15 minutes. It has great support for always-on sensors using the new Hexagon 680 DSP.
The Qualcomm 821 was designed from the ground up for these new generation smartphones. The Google Pixel takes advantage of that capability to improve the camera's image quality performance and the most important part is to use it to support the device mobile VR capabilities. Developers can create high-quality games for Daydream, knowing that the platform will pose little limitations. It's not the fastest phone on the planet, but it provides the needed performance to back up the Google Pixel's advanced features, like the Google Assistant and the Daydream mobile VR platform.
The Qualcomm 820 was criticized for getting too warm while multitasking and this also had an impact on the battery life. The new Snapdragon 821 is more power efficient and we can just assume that Qualcomm solves that thermal issues.
The Qualcomm Snapdragon 821 can't beat the Apple iPhone 7 A10 if you are just wondering. Google Pixel scored 1580 in the single-core test and 4100 in the multi-core test in Geekbench 4 benchmark, while the iPhone 7 tops it by quite a large margin with 3430 and 5600 score respectively.
So not the best CPU, but one that supports all the great features that Google wanted you to enjoy with this new phone and it can obviously run the latest and future high-demanding games and apps.