In a recent software update, Amazon has added the ability for the Amazon Echo to connect to external Bluetooth speakers. The Echo Dot has always had this ability because you’re expected to connect it to external speakers, but the full sized Echo is meant to be a stand alone device, so external speaker connectivity was never present until now.
If you’re unhappy with the performance of the Echo’s built-in speaker, you can go into the Alexa app and connect it to better speakers, as long as they support Bluetooth. The Echo Dot also has an auxiliary 3.5mm audio out connection, but that is not present on the full sized Echo.
Amazon has been on a trend lately of unifying functionality across their Alexa devices. The Amazon Tap recently gained hands-free Alexa functionality, which was previously only present on the Echo and Echo Dot. Now the Echo has gained functionality that was previously only available on the Echo Dot.
There’s a good chance the expansion of the Amazon Echo’s Bluetooth functionality is somehow related to the audio synchronization functionality that is expected to arrive soon. The leaked images of audio sync settings in the Alexa app state that the feature interrupts active Bluetooth connections. I would guess that Amazon needed to enable external Bluetooth speaker support for the Amazon Echo in order to make audio syncing work.
See Amazon’s help page for full instructions on connecting the Echo to Bluetooth speakers.