Originally Posted by
daveland
K for Hawaii; M for anywhere else domestic. (K is also the minimum class for a companion upgrade.)
Sorry,
It's K anywhere domestic or within North/Central America:
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Travel within or between the 50 United States, Bermuda, Canada, the Caribbean, and Mexico on any published fare booked in Y, B, M, H, Q, or K class. For all other international travel, upgrades are valid on any published fare in Y, B, or M class.
https://www.delta.com/skymiles/about....jsp#medallion