https://www.theverge.com/circuitbreaker/2017/8/29/16219876/amazon-multi-room-speaker-playback-echo

Amazon Echo devices can now handle music playback across multiple rooms. The company announced today Echo users can now synchronize music across devices in their home. Later, this feature will extend to controls for multi-room music on other connected speakers.

For now, the Echo devices — including the Dot, Echo Show, and regular Echo — can only handle music requests from Amazon Music, TuneIn, iHeartRadio, and Pandora, but support for Spotify and SiriusXM is coming soon. Amazon also says it's launching new developer tools for speaker makers who want to make their devices compatible with multi-room playback. Alexa Voice Service (AVS) Multi-Room Music SDK allows device makers to integrate with Amazon Alexa Multi-Room Music; this tool will be available later this year.