As detailed in this Flyertalk thread, and discussed by One Mile at a Time, beginning this coming Tuesday Delta and Northwest will begin offering reciprocal upgrades — Delta elites will receive automatic complimentary upgrades on Northwest, and Northwest elites will receive automatic complimentary upgrades on Delta.

DL/NW Reciprocal Upgrades Are On The Way!
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October 23, 2008

On October 28, 2008, SkyMiles and WorldPerks elite members will be eligible to receive complimentary upgrades on Delta and Northwest flights.

Reciprocal upgrade is for the elite members only.

SkyMiles companions will only be eligible for upgrades on DL coded and Delta operated flights.
WorldPerks companions will only be eligible for upgrades on NW coded and NW operated flights.

What is changing?
• Beginning October 25 you will start to see V/X inventory being added to some DL coded flights operated by NW. Even though you see the inventory, the upgrade won’t be applicable for travel before October 28.
• On and after October 28, SkyMiles and WorldPerks Platinum, Gold and Silver members will receive a complimentary upgrade on applicable DL or NW coded flights which are operated by DL, Delta Connection, DL Shuttle ( effective when F/C reconfiguration is completed ~ Dec ’08), NW or NW AirLink (Mesaba, Compass, Pinnacle)
• Customers on delta.com will be able to add their frequent traveler number for any airline program to their new or existing reservation
• When a NW elite number is added to the PNR with applicable DL or NW flights, the upgrade will automatically be requested
• When a DL elite number is added to the PNR with applicable NW flights, the upgrade will automatically be requested
• NW elite status will be printed on the boarding pass

What stays the same?
• Area of travel: within/between the U.S. (excluding Hawaii) and Canada, Bermuda, Caribbean, Mexico, Central and non BusinessElite markets in South America.
• When a NW elite number is added to the PNR, the NW Platinum, Gold or Silver status will be shown in the SSR (this became effective in September)
• Clearance is based on member status and booking class. If status and paid class are the same, time of request will determine clearance order.
• Pending upgrade is automatically added to Airport Standby List
• Upgrades booked in G/Z class