Night Sight 2.0 with a new astrophotography mode, Live Caption and offline Google Assistant are just three examples of features debuting on the Pixel 4 series. However, these will not remain Pixel 4 exclusives, with Google planning to bring them to older generations too. We have laid out Google's plans in a brief overview, underlining that you need not buy the latest tech to get the latest software.
https://www.notebookcheck.net/Google-to-bring-at-least-five-Pixel-4-to-the-Pixel-3-and-Pixel-3a-series.440125.0.html