Hinge looking dropouts
 

Do these have any special function like suspension or passing in a belt? It’s not really clear if they do come apart.

I don’t know which coworker owns this very pretty Rex or I’d ask. I hope I can afford a Rex someday before he retires.

https://cimg9.ibsrv.net/gimg/bikefor...42381c52a.jpeg
https://cimg0.ibsrv.net/gimg/bikefor...ffa859c3e.jpeg
https://cimg1.ibsrv.net/gimg/bikefor...661d3f02f.jpeg

One more

https://cimg0.ibsrv.net/gimg/bikefor...14aed5ff3.jpeg

A couple things:
1 - It may come apart but doesn't really look like it given the paint.
2 - Those seatstay look like carbon fiber and not steel like the rest of the frame. That end is probably epoxied to the dropout that is brazed into the chainstay and would have some adjustability (See 3 below).
3 - There are dropouts with pivots as shown in the picture that provide adjustability for the angle of the seatstay attachment point. Dropouts with fixed angles between the chainstay and seatstay attachment points usually come in only a couple angle configurations. For small frames this is a problem.

Cost is the big reason to use a dropout with an adjustable seat stay angle. One SKU for all frame sized. Minimal joining prep. And it works very well.

This type of stay attachment has been done for many decades, Raleigh's DL-1 (their rod brake 3 speed bike) might be the most common example of this (and this model was called by a Raleigh sales rep as being the most popular bike they make, if you include all the examples made in the 3rd world under license).

Cast Dropouts This is a link to Ceeway's site and about 2/3s of the way down the page are a number of "Articulated Angle" dropouts. Andy

That's the description I was looking for!

Steve (Rex) used to have an option for a carbon rear end. This appears to be one of those. They may have had a multiangle option so he could customize the rear triangle. That is a nice looking Rex but an older one, and the Tiagra rear mech is a little surprising.

Dedacciai sold a carbon rear triangle with separate chainstays/seatstays. They were both in a wishbone, a lot like 2 forks. They had parts to join them to a metal frame. Nova used to sell them, they weren't all that expensive. We can't see the bb or seat cluster, that would give more info. I always thought about buying one of those rear triangles, but never did.