According to a helpful commenter who provided this photo, a Walmart (location unknown) is currently selling Xiaomi's not-actually-out-yet Mi Box. The price? $69. Not bad at all - great, even. Xiaomi has not indicated when it plans to release the device specifically, but if this is any indication, you can probably guess "pretty soon."
So, it may not be a bad idea to call up your local Walmart and see if they made the same mistake - this could be more widespread than we know. And at $69, that's an easy impulse buy, am I right? The Xiaomi Mi Box does 4K and, according to the box, even comes with an HDMI cable. That's handy.
We'll be reaching out to Xiaomi to see if they can confirm the price, release date, or any updated availability information. But at the alleged cost of a Chromecast Ultra, it's easy to see these things selling like hotcakes.
Here it is being unboxed.