So I'm booking a trip FLL-SFO on delta.com and it offers me the choice to upgrade to first class for $170 each way (not bad I suppose) or for a whopping $644.50 more each way the convenience of changing my ticket whenever I want (Flex This Fare)".

I realize the First Class upgrade offered for $170 probably doesn't allow changes, but wow, $644.50 each way just for the privileged of being able to change the itinerary at will!

Many business people fly only on fully refundable/changeable tix. If you look at the difference between the cheapest fare bucket and full Y on a fairly typical domestic USA flight, it can often be 9-10x.

Given any "regular" ticket is changeable for a fee and perhaps the fare difference, I'm wondering what the advantages are of buying a Y fare (automatic upgrade to First perhaps).

"For just $8,570,000,000 more, you can buy this company."

I am sure there are legit times when a late ticket is purchased and the travel plans are very uncertain that it can make sense.

But I would bet that the vast majority of full Y fare tickets are either because they are the only fares left, or more likely it is somebody traveling on corporate cash who wants the upgrade.

For years the company I worked for allowed this to go on. When they finaly stopped allowing it, the salesmen were crying for months.

You can change them as many times as you want, where if you change a cheaper ticket multiple times you may end up paying multiple change fees. Also, tickets issued at flexible fares are usually fully refundable as well, whereas cheaper tickets are only returned in the form of an eCredit.

The "flex this fare" option doesn't necessarily give full Y tickets. Often it gives you a B fare, in markets with refundable B, which is changeable but does not give the instant upgrade to elites or put one ahead of everyone on lower fares in the priority list for free upgrades.

I wish the food in FC looked that good

Delta is obviously not thinking large enough!

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Any fare class can be refundable. I have seen them as low as K class....mostly in direct competition with WN.

I know, but I think people need to be warned that despite what they might assume, "flex this fare" doesn't necessarily book into Y with the expected upgrade priority. Nor does it always give the cheapest flexible fare. In fact, it would be interesting to do some experiments on markets with refundable K fares.

Also, I've noticed that delta.dumb sometimes gives a lower fare for exactly the same flights on the same dates when you do advanced search from the start with the refundable/flexible box checked compared to picking flights and then checking the "flex this fare" box.

If you want full Y, it's better to search from the beginning by fare for Y or higher with the
refundable/flexible box checked on advanced search.

The bottom line is that you should never purchase the "flex this fare" option without investigating whether you can find a better ticket on delta.dumb.