There are no changes to the way SubD to NURBS conversions work.
The ToNurbs command will continue to create non-rational cubic NURBS surfaces.
The ExtractWireframe command will continue to create non-rational cubic NURBS curves.
Away from extraordinary vertices, the conversion to NURBS is geometrically exact.
Near extraordinary vertices the NURBS conversion is approximate.
This behavior is identical to the SubD to NURBS conversions in Rhino 7 and Rhino 8.0.
The NURBS patch density is higher near sharp edges.
The Rhino SubD sharp edges algorithm is the industry standard Catmull- Clark subdivision surface sharp edge algorithm described in Section 3 of Subdivision in Surfaces Character Animation. Rhino’s version assigns a sharpness value to each end of an edge (the citation above assigned a single value to an entire edge.) For edges with constant sharpness, the Rhino SubD result is identical to what is described in the citation. For variable sharpness edge chains, the Rhino SubD result is similar but has slightly better curvature behavior in common modeling situations. Rhino’s approach also permits a single edge to have variable sharpness.
SubD surface tangent and curvature are continuous across smooth and sharp edges.
The user experience is to select edges and assign sharpness at vertices in the chain. These user supplied values are used to set the edge-by-edge sharpness values.
You may follow the development progress by looking at these Rhino YouTrack issues.
https://mcneel.myjetbrains.com/youtrack/issue/RH-73321
https://mcneel.myjetbrains.com/youtrack/issue/RH-73322
https://mcneel.myjetbrains.com/youtrack/issue/RH-73323