Google Pixel features an F2.0 aperture lens, which is slower than some other high-end phones. For example, the LG G4 and new the iPhone 7 have a f/1.8 lens. This is a third of a stop difference in favor of the F1.8 lens or 0.304 stops to be very precise. In other words, the iPhone 7 lens of its primary camera results in 1.2x times more light to pass through than the Pixel's primary camera. The Samsung Galaxy S7 features an even faster f/1.7 aperture lens.
You might assume that this means that the Google Pixel camera is inferior to the iPhone 7 camera for low-light shooting, but this is not the only parameter that should be taken into account. The pixel size, sensor technology and optical qualities of the lens, all pay an important role in improving the low-light performance of the camera.
For example, the Google Pixel camera features a 1.55-micron size pixels. The Samsung Galaxy S7 sensor has 1.4-micron size pixel, smaller the Google Pixel camera image sensor. There is also the software side that can also helps to improve image quality of images shot under restricted lighting conditions, like the new HDR+ shooting mode in the Google Pixel and Pixel XL, that can captured a sequence of images, layer and analyze them to produce a single image with better exposure and less visible image noise.
We still need to wait and see how the Google Pixel f/2.0 camera copes with the other high-end devices in real-world tests, but the specs, DxOMark image quality tests for Google Pixel and early sample images look very promising.