Originally Posted by ranskis

Exactly, this is flexible for changes.
However, the fare is not refundable, so in case the flights are not cancelled, you cannot get your money back.
This is a promotional fare with 120 days advanced purchase, you need to book by 31MAY.
This means that if you want to make changes before departure, you are subject to the fare difference with the new fare available at that moment. I guess there will be good deals for a while this year though but the new fare might be less flexible. You can also change it to another origin if there is a promo that suits you at the moment you make the change, like changing AMS BOS for BRU SFO.
However, once you have flown the outbound (no stopover permitted) you can change for free the return leg with the historical (cheap) fares and without penalty, and you can do it several times (max stay is 3 months), the fare will be recalculated but just as if you had bought it now in the first place. So as long as you know when you want to go to US, you don't need to decide exactly when and how you go back, pretty cool.