They're definitely showing you historical prices from their cache. Kayak gets such a huge volume of traffic that they can use the lowest price on that route see

They're definitely showing you historical prices from their cache. Kayak gets such a huge volume of traffic that they can use the lowest price on that route seen in the last 24 hours and have pretty good coverage/accuracy. Personally, this thread is eye opening because I work on a similar product. I saw this when it came out (a couple weeks ago maybe). My first impression wasn't that it was particularly impressive, but apparently I just don't know what's cool for users in a travel product =P