If we are to believe the latest rumors, older Chromecast models will also have access to multi-room audio. It concerns the models of the second generation, as well as the Ultra model. The first generation will not get the support anyway.
Multiroom audio for older Chromecast models – rumor
The latest version of the Google Chromecast offers support for multiroom audio. This makes it possible to listen to the same music in several places in the house, where speakers are located. You can send the music to the dongle, but also to speakers with the technology on board and smart speakers, like the Google Home Max, for example. And as it looks now, the Chromecasts of the second generation also have access to multiroom audio. The same applies to the Ultra model.
This rumor comes out via Reddit where a use has had contact with Google’s customer service. In the response of the employee is therefore which Chromecast models may count more on multi-room audio. Although no release date is given, the answer states that this must be done “before the end of the year”. Since Google did not publish this news itself, we have to take the news for a while with a grain of salt, unfortunately.