Amazon and Google have had a fairly strained relationship over the past few years, despite Amazon using Android as a base for their hardware devices. You can’t buy a Chromecast on Amazon, and Amazon Prime Video was a holdout on Google Play devices for years.
Things have been shifting (slightly) recently, with Amazon finally bringing its video to the Play Store and being more receptive to standard Google practices. And now, Amazon has quietly added Chromecast support to its Amazon Music app, at least on certain phones.
Right now, it looks like it’s only working on the Pixel 2, including older Nexus phones. It could just be a slow rollout from Amazon, but they’re not very transparent so it’s anyone’s guess at this point.
Amazon’s Android reliance is weird, but it’s pretty clear that the retail giant is in direct competition with Google on many fronts: Google Home vs Alexa, the Fire Tablets vs Android tablets, and Amazon’s digital storefronts vs Google Play. It’s sensible for Amazon to hold out some features to promote their own ecosystem, but those walls have slowly been coming down and hopefully this is a sign of that speeding up.