The Google Pixel 3 and Google Pixel 3 XL are the standard bearer of all Android smartphones. Launched with the latest version of Android, Android Pie, the Pixel 3 flagship duo bring the latest and the best of Google's software prowess to the masses. Google tends to launch these phones with exclusive new software features, and the same software features are then rolled out gradually over the months to older Google devices. Even though the older devices may be fully capable of utilizing such features, an exclusivity period acts as an added incentive for potential customers for the newly launched devices.
One such exclusive feature is Top Shot. Top Shot takes a burst of images rapidly, and then utilizes machine learning to point out the best shot in the series. This best shot will usually be instances where the subject is smiling, blinking and/or looking at the camera. This takes away some of the pressure of timing a shot well, and gives more confidence to the end user to actually capture useful and useable images. Combined with the excellent camera performance on the Pixel 3 flagship duo, the end result is that Google has a rather compelling incentive.
But as it turns out, you can enjoy Google's Top Shot feature on your older Google Pixel 2 and Google Pixel 2 XL right now. As found out by Reddit users /u/FuegoInfinito and /u/rayw_reddit, you can activate and use this feature on the Pixel 2 by simply sideloading the Google Photos app from the Pixel 3. This is indeed a strange discovery, as the same Google Photos version available publicly does not make Top Shot work on the Pixel 2 (and you are not doing any apk hacking here, either).
The Top Shot feature becomes available when browsing photos in the Google Photos app. You can view Top Shot samples taken with or without XDA Senior Member cstark's modded Google Camera app. You may need to uninstall the updates to the Photos app as the Google Play Store may have updated the app with a higher version number, which would stop you from installing the apk from the Pixel 3. To clarify, you do not need to completely remove the Photos application from your Pixel 2, but you may remove the updates to the app to allow seamless sideloading of the Pixel 3 Photos app.