Thanks very much for your response. I'm afraid that I have caused some confusion here by not being very clear on what I'm after. I apologize.
When I say "spec" I am referring to the Swagger specification file that defines the API, and is subsequently used as to generate the documentation, the server stubs, and client bindings. This is a YAML file or can also be interchanged as JSON. It is this file, literally the specification of the API, in which I'm interested. It was formerly called the Swagger Specification but is now called the OpenAPI Specification.
This file can be used as an input to the Swagger Codegen client generation tool (or other tools). See here:
With the specification in hand, client source code can be automatically generated targeting a large number of languages and the client needn't be coded by hand.
I've searched the web and the Ultimaker github repos, and I have not been able to find it.
Is it possible to get this file posted somewhere?