A cabin class (F/J/Y or First/Business/Economy) can have multiple fare basis within it, which are designated with specific letters.
For the app I am developing, I need to determine the cabin class of a specific fare basis for a given flight. I am using GetItinerary (Service action code: TravelItineraryReadRQ) since I use a PNR, but although it gives the fare basis, I can't seem to find the cabin. I am pretty sure Sabre has a way of telling, since BargainFinderMax allows you to search through different cabin classes. Any ideas?
Having the class of service you could check the DU table with VendorCodesLLSRQ to see which cabin it corresponds to for that specific airline.
https://developer.sabre.com/docs/soap_apis/utility/get_vendor_codes/
Hope this helps. Bruno.