CHASE, TODAY? First things first: That giant bonus comes from the Chase Sapphire Reserve card. Here’s how it works (and don’t confuse it with the similarly named Preferred card): If the bank accepts your application, you have three months to spend $4,000. Once you do, Chase hands over 100,000 of its proprietary rewards points. Then you can trade them for $1,500 worth of travel, as long as you book your flights or rooms through Chase.

The card has a $450 annual fee, but it gives back $300 of it each year once you purchase at least that amount in travel. It also gives out a generous amount of points — three per dollar spent — on travel and dining. Plus, you can swap points for miles on many airlines if you want to take your chances with seat availability in those reward schemes. Other perks include access to some airport lounges and a rebate for fees you pay for TSA PreCheck, the expedited security screening, or Global Entry, which speeds international returns.

In cardland, any offer this lucrative tends not to last. This week, Chase said it would cut the 100,000-point bonus in half for anyone who applied online after Jan. 12 or in a branch (which isn’t possible for people in parts of the country where there are no Chase branches) after March 12. To be safe, the company suggests applying online by Jan. 11, before it flips the switch the next day.

Why the change of heart on a product Chase introduced last summer? The company always said the bonus was an introductory offer, and the bank’s generosity led to a $200 million to $300 million hit to its earnings. So the window on a good thing is partly closing.

So should you take advantage of it while you can? My wife and I both have done it and are glad we did. It has required some mental energy to channel the right amount of spending away from our current card and track the new bills so we don’t end up paying late. But there is nothing that focuses the mind quite like feeling that you are beating the system.