The sale covers a large window of travel that is open through May 2017. The only blackout period for the fare sale is over the Christmas holiday (December 14-23) otherwise there is plenty of inventory.
The best fares are predictably from the East Coast where Boston to Amsterdam can be booked for only $630. Fares from New York to most SWISS destinations in Europe range between $750 and $900.
From the West Coast, the best deal is to Paris which can be booked for only $750 from Los Angeles or San Francisco.
Based on the info I have, I don’t know when the fare sale ends but I can say that a Saturday night stay is required in order to receive the best fares.
