Spotify’s Mac and Windows apps can now start streaming to Chromecast devices. Previously these apps have been able to control pre-existing Chromecast streams. Instead, you had to start a Chromecast stream on iOS or Android, before it could be controlled through the desktop app.
You can start a Chromecast stream on the desktop apps the same way as a Spotify Connect stream. You can select between your streaming devices, which now include Google cast as well as Spotify Connect-enabled speakers.