As far as I know generative design it modified through Dynamo and not exposed through the Revit API. So I assume the path would be you write a zero touch node for Dynamo and integrate that into a generative design Dynamo graph.
The starting point for looking for API's for other Autodesk applications is the Platform Technologies section of the ADN site:
https://www.autodesk.com/developer-network/platform-technologies
I've a vague recollection of Fusion without the 360 part so not sure if below is what you are looking for...
http://autodeskfusion360.github.io/
