Originally Posted by
jackal
I believe DL considers Central America as "domestic" for the purposes of upgrades. It's Europe/Asia/Africa/Australia and at least deep South America (if not northern South America) that are ineligible for automatic complimentary upgrades.
I have heard it explained that any route served by an aircraft without an international biz cabin is elegible for comp upgrades. I don't honestly know DL's international routes or aircraft well enough to know if that is entirely true, but I believe that domestic routes including Alaksa (but excluding Hawaii), almost all (if not all) of Central America and the Caribbean, and select South American routes are included for comp upgrades. I don't think their routes within Asia are included...but I'm not sure.
From
delta.com explaining Medallion complimentary upgrades (AS upgrades may be different):
Complimentary Upgrades
Your Medallion membership entitles you to enjoy unlimited complimentary upgrades, subject to availability, on most published economy fares on Delta and certain Delta-designated codeshare flights in North America within or between the United States (excluding Hawaii) and:
Bermuda
Canada
Central and South America (1)
the Caribbean
Mexico
(1) Exceptions apply for this area of travel. See terms and conditions:
Unlimited Complimentary Upgrades are subject to availability, may not be available on all flights or in all markets, and are not valid for travel to/from Hawaii, Transatlantic and Transpacific destinations. Complimentary Upgrades are not available on flights to/from South American cities that are serviced with our BusinessElite® product (i.e., Buenos Aires, Argentina; Rio de Janeiro and Sao Paulo, Brazil; Santiago, Chile; Lima, Peru; Caracas, Venezuela).