https://www.cnet.com/news/amazon-echo-input-is-a-tiny-35-dot-for-your-own-speakers/

Just like the Dot it uses Bluetooth and a 3.5mm analog audio connection to mate with speakers. And just like the Dot those speakers need to be powered themselves, or connected to another powered device like an AV receiver.

The Input stands just 12.5mm so it can easily hide in the room, and Amazon touts its four-microphone array "so you can talk to Alexa from across the room."