I haven't seen it myself, but a lot of people took a screenshot before Amazon deleted the tweet. Here's one:
— Jeff Park (@jpark40) September 12, 2016
The link mentioned in the tweet leads to the Amazon listing for the current Echo Dot, which is no longer available. That device cost $90, and it was basically a version of the Echo which only had a small speaker.
It was supposed to be hooked up to your sound system via the included audio cable or Bluetooth, and it had all the same voice command features as the $190 Echo, including playing audiobooks or reading news headlines on command.
Of course, that was the old model; we don't know yet what the new Echo Dot can do. Will the new hardware have new features, or does the lower price reflect a less capable device?
Amazon isn't talking, but a recent rumor suggests that Alexa might soon listen and respond unprompted. That might be a feature on the new Echo Dot.