To take advantage of the change, make sure the Sonos app is updated. Under Settings, select Services and Add a Service under Music & Content. You’ll then be able to stream through the Sonos or Spotify apps, or you can start a playlist with Google Assistant on voice-enabled devices. Alexa does not yet work with Spotify Free.
This is undoubtedly a pre-holiday push to make Sonos speakers more appealing to the millions of people who use Spotify Free. Given how many users stream for free, it’s honestly surprising that Sonos did not support this before.