Wow, this is a pretty good price for ZRH and especially as it doesn't have promos as often as some other cities...GVA seems to have the promo as well.
I looked at the fare rules on AF/KL and strange thing there is no deadline under Category 15: Sales Restrictions. They could pull the fare at any time, but it seems like there is not the same purchase deadline of 31st May like on OW?
Also, seems like more choice of flights at the lowest fare on Matrix when you put a US sales city...replicated when I searched on klm.com which mainly gave me DL flights at the best price vs. airfrance.us which gave more AF/KL flights at the promo price.
In any case, I bought ZRH-SFO return on KL Business for about CHF 300 less back in January...that was a good promo!