One of the biggest perks for many frequent flyers is the complimentary upgrades that come with elite status. At the highest end of privilege, members of legacy airline loyalty programs enjoy space-available, free upgrades to premium cabins in most domestic markets and certificates for the occasional international upgrade.

As loyalty programs have evolved over the last few years, however, those upgrades have been harder to secure. On the availability side, fewer upgrades are now open because airlines are now aggressively pricing premium cabins and actually selling the seats. When the seats do become available for upgrade, the process is also now harder.

Recently, American changed its upgrade policy to prioritize higher-spend travelers when considering two passengers at similar elite tiers. And both Delta and United recently took away complimentary upgrades for frequent flyers on the majority of premium transcontinental routes.

Now, Delta is reversing that policy. In a series of updates announced to its premium cabin customers last week, Delta said it would be bringing back same-day, complimentary upgrades on premium transcontinental routes — even those that operate with lie flat seats.

The upgrades will be limited to the day of travel and won't clear in advance like typical elite upgrades. However, each premium seat will theoretically be filled with a paying or elite passenger under this new policy. Like typical complimentary upgrades, priority for the open seats will also fall to highest-tier Diamond elites first, so low-ranking SkyMiles members may find an upgrade unlikely.

Still, Delta's move last week may be an indication that it is willing to start giving more perks to its premium SkyMiles members. As Delta's loyalty program has shifted to a revenue-based model over the last several years, SkyMiles and the perks that it offers have contracted significantly to keep profits high. American and Delta too, have made similar moves.

Instead of profits, Delta now seems to be more motivated by competition. JetBlue's premium Mint cabin has been making inroads with business travelers as many start considering product over loyalty. And all three legacy carriers have boosted catering options on transcontinental routes, largely in an effort to claim that they provide a marginally better product.

With free upgrades now in play for some SkyMiles members, Delta has a temporary competitive edge over JetBlue and United. American already offers the upgrades. Once the other carriers reach parity and provided profits stay strong, Delta would likely move onto the next small incremental improvement.