Two cool new features of the Pixel 4 camera will not be ported back to older Pixel phones – Live HDR+ and Dual Exposure Controls. Those can only run on the new hardware, so the Pixel 3, 3a and others are out of luck.
To be fair, few phones are fast enough to do real-time HDR preview. The Pixel 4 and 4 XL technically aren’t either, what you see on their viewfinders is an approximation of the final result. The effects of the Dual Exposure sliders are previewed in real time so they aren’t supported on older models either.
— Made by Google (@madebygoogle) October 21, 2019
Google is throwing the Pixel 3 and 3a a bone, however – the astrography mode called Night Sight will be backported to older models. It can snap up to fifteen exposures, each 16s long, correct for the motion of the stars and the swaying of the trees and output an impressive shot of a starry sky.
But obviously there’s no real-time component here. Chances are that the live preview duties are handled by the new Pixel Neural Core and can’t run on the old Pixel Visual Core.