Hello,

the information models are so far have version information included in the offline XML nodeset notation like in https://github.com/OPCFoundation/UA-Nodeset/blob/master/DI/Opc.Ua.Di.NodeSet2.xml.
"
<Model ModelUri="http://opcfoundation.org/UA/DI/" Version="1.01" PublicationDate="2012-12-31T00:00:00Z">
<RequiredModel ModelUri="http://opcfoundation.org/UA/" Version="1.03" PublicationDate="2013-12-02T00:00:00Z" />
</Model>
"

However, as far as I know, only the namespaceURI is visible at server's runtime, the URI stays unchanged with version updates. At some point of time the evolution of some companion will probably make some incompatible jump where client and server might interpret different models based on the same URI.

Question is: how is versioning of models and types addressed in the standard? How can a sever/client support multiple versions of the same model? Do the version have to be matched during connection hand-shake?

One "quick-hack" to (at least) indicate the used model/namespace version would be to use semantic versioning (https://semver.org/) and include the version into the URI string e.g. "http://opcfoundation.org/UA/DI/#v1.01" that is exposed in the NamespaceArray. It would however require clients to ignore/evaluate the semantics the the URI-suffix.

Best Regards
Sten