With the OrganizationData.svc, the URL was always <baseurl+org>/XRMServices/2011/OrganizationData.svc
The replacement for WebAPI is <baseurl+org>/api/data/v9.1/
Or v8.0, v8.1, v9.0, etc...
So the question is, will all JS and any other WebAPI calls in code need to be constantly updated w/new releases?