According to some delving into the code behind a recent Google App update by 9to5Google, there appears to be some loose coding infrastructure in place for a line of Google headphones, under the name "Bisto".
According to some of the deductions made on the code found, these headphones would be made by other manufacturers but would run Google Assistant. This speculation arose by using a technique known as APK teardown, which involves taking apart the latest version of an application, usually an Android app, and examining lines of code that then might describe or suggest intentions from the developers. With that being said, all of this might already have been ditched by Google, but many news sites believe that Bisto headphones are coming.
As already mentioned, the actual headphones would be made by various manufacturers and Google would be providing the optional software and backend. The code suggests that notifications could be read aloud through Bisto headphones, but this wouldn't happen automatically, there would be a soft chime which would indicate a notification had arrived, the user could then press and hold a button to have the notification read aloud to them.
This same button would then be used in order to verbally reply to notifications and appears to be a push to talk arrangement that has been used in phones in the past. Bisto could also have a briefing function where an update on key information, like battery level, weather, and time, can be requested by the user.