I have just notice a SUBD tool in Rhino 6 video on Youtube.
Is this a new tool? or is it a plugin?
It was in the V6 WIP. It’s still in the WIP (V7) but not in the released builds of V6.
There is a SubD discussion category.
It actually is in the Rhino 6 release but seems to be a hidden feature as I guess it’s still WIP.
The commands don’t autocomplete but still run. So use at your own risk I guess.
lokks a bit like Clayoo or Tspline of late
It’s working on v6 released just the command line was hidden from list
Im coming from Lightwave 3d where there have been SubD’s for ages, so Rhino is really confusing me atm.
Hopefully someone here can help me out a bit so I can get over the initial learning curve of Rhino that bit faster.
Thanks in advance.
Just to begin with, how can i turn these two planer surfaces into subD’s? As far as i can see i can’t, so how am I supposed to fill this hole in the sphere?
Lightwave id just weld the points and SubD it. 
Moved thread to Serengeti > SubD category
No? what am I missing here?
Whats the technique in Rhino?
@Enscaped McNeel is currently developing a set of Sub-D commands for inclusion in Rhino, but they are not yet mainstream.
Are you interested in non-Sub-D methods to fill the hole? If so then possibilities include Untrim, EdgeSrf and Patch. Describe your design intent and post a .3dm file with the geometry if you want someone to provide more specific suggestions.
Thanks for the reply,
Yes, I am interested in non SubD methods, as they are the only methods to resolve this as far as i can see.
Isn’t that what I asked in the first place?
So Untrim, EdgeSrf, and Patch are the kind of direction I was hoping someone could give me. I have modeled using tri-planers, edge modelling, etc, before. Untrim is a new term, I will look into that, thanks.
Basically, as a method of learning Rhinos UI, I took a NURBS sphere, used CutPlaner to divide that sphere into three parts. When I cut the sphere I was hoping that Rhino would create a new surface where the cut was made, but it didn’t, so now I’m left with three pieces that have surfaces missing. So, again, as a way of understanding Rhino, I now want to add the surfaces that are ‘missing’.
At the moment that is all I am trying to do. I guess I am having to unlearn to learn, if that makes sense.
Trim or Split the sphere and cut plane with each other, and Join. An alternative would be to use BooleanDifference on the sphere and cut plane, but you should also be comfortable using Trim, Split and Join.
Also investigate Wirecut
You may find it worthwhile to go through the Users Guide which is an intro tutorial, and the Level 1 and Level 2 training manuals.
Thanks David.
I will look into these suggestions If i mange to find a few spare minutes. 
Further discussion on non-subd modelling please in a separate, new thread. Thank you.
Sure.
so it’s like in the released Rhino6 we can’t use Subd?
no, use v7 beta to use the subd tools.