While I know (having read posts in the Delta/SkyMiles Medallion FT forum) that SM members have been successful at using their SM miles and/or Upgrade Certificates to upgrade to "DeltaOne" (for DL-operated flights) or equivalent business class (on partners-operated flights such as AF), they were bound to look at upgrades/awards inventories from the flight that was marketed, so:

- if the flight was purchased via DL, no problem, the upgrade/award fare needs to be available on the DL-XXXX coded flight.

- if the flight was purchased via AF, even if operated by DL, in order for the upgrade to clear, upgrade/award availablities need to be made on the AF-XXXX coded flight.

Of course, whether you pull inventory (using KVS or ExpertFlyer) for a flight using the DL-coded flight or the AF-coded equivalent flight would yield different results, esp. in terms of awards. AF's Yield Management might release awards/upgrade fares ("O") on its "natural" coded flight, but not on the partner codeshared equivalent flight.

Assuming the reverse is true and FB is able to tap into the upgradable fare class of your AF-operated flight, FB would still be bound by DL upgrade chart and DL fare classes (here "G") rules for you to upgrade. Therefore, not sure that availabilities in "O" matters here, because what counts is whether the equivalent of "O" in DL fare class system is available.

At the end of the day, this sounds rather complicated and you would be luckier if using your SM miles (if you have any) to upgrade your DL-coded flight / AF-operated flight (in that direction it is possible).

That, or, upgrade with cash at OLCI when you do it H-30 on the AF website with your 006 eTicket number (or your AF equivalent PNR if you know it – you can ask Delta for the AF mirror PNR code).

Good luck!
vinnyc