Since Google’s Cast standard has been around for a while, it’s not unusual for people to now have a sizable collection of speakers and displays that are compatible with it. Google seems to be experimenting suggested cast devices to assist you find the one you might be looking for.
Update: New information from Google has been incorporated into this piece.
In most circumstances, Google Cast is managed by Android itself, and when the Chromecast icon is clicked within an app, a pop-up menu displaying the list of targets appears. Although there are few exceptions, such as Spotify, this UI is typically employed and is the foundation upon which Google is built.
Some users have begun to notice that Google now displays one speaker at the top of the Cast list in the Suggested section. As the feature was being used with YouTube Music, the ChromeUnboxed team emphasized it. The feature seems to have started appearing for a few people during the past two weeks or so. The feature has not yet been seen on our devices. It appears to be a server-side rollout that is only partially implemented.
Update 5/25: According to Google in a conversation with The Verge , only YouTube Music is introducing support for Suggested devices in the Cast menu. As of this week, the modification has been fully rolled out to all users. Suggestions are based on usage, history, and the type of device, which is very similar to our own theory.
What motivates Google’s suggestions for this list is currently unknown. The speaker and your phone are typically not in close proximity to each other for existing Cast targets. It appears much more likely that this will be determined by your casting preferences, with frequently used speakers appearing in this new section or possibly dependent on the time of day. Whatever the case, it appears to be a fascinating new feature.