A couple of years ago, Microsoft officially confirmed the existence of the Xbox "Keystone", confirming in May of 2022 that the company had decided to "pivot away from the current iteration of the device" and find a new approach.
The Keystone was a streaming box that would let you play Xbox Cloud Gaming titles on "any TV or monitor without the need for a console", and a newly-discovered patent reveals what it might have looked like (thanks, Windows Central).
In the images (more of which are viewable via the patent), the Keystone is shown to be a small, square box that closely resembles the Xbox Series S. It comes with a USB port, power button, ethernet port, HDMI port and pairing button.
As far as we know, the Keystone isn't still in development at Microsoft. Xbox boss Phil Spencer mentioned in late 2022 that the original design was too expensive to make (the goal was to sell at around $99 - $129), but the company was still committed to finding a solution at the time. Since then though, talk about the Keystone has gone very quiet, aside from the device being spotted on Phil Spencer's shelf in a video last yeaar (as you can see above).
This thing may never see the light of day, but it's nice to see what it might have looked like!