If you manage to book it with an AF flight number, you should be able to have a free bag, as per:
https://wwws.airfrance.fr/en/informa...res-air-france
Traveling with our partners
To offer you even more destinations and additional services, Air France partners with airlines that share its high standards of safety, comfort and quality.
When you travel with SkyTeam alliance members
as well as on flights provided by our many partners,* you enjoy the following Air France advantages:
- A digital press selection is available at no extra charge on the Air France Play app via your tablet or smartphone.
- Flying Blue members earn the same number of Miles as when traveling on an Air France flight.
- Are you a Flying Blue Silver, Gold or Platinum member? You may check in an additional baggage item at no extra charge.**
* Flights provided by a partner airline with an Air France flight number
** Not including flights provided by Alaska Airlines, Belavia, Bangkok Airways, Etihad, Finnair, Gol, Jet Airways and Luxair
KL has no similar statement on its own website:
https://www.klm.com/information/tick...rtner-airlines
I would be pretty confident that, departing from AMS or CDG, they will check one bag for free to your final destination.
But good luck on your return flight, if you face a BT agent who wants you to pay a fee... especially as AF website may show conflicting information on different pages...