Disclosure: I own another competing flight search tool, https://concorde.io
Even if assume the other fares and the lowest published fare do track there is still an issue. Hopper doesn't/can't track or predict seat availability, so when Hopper gives me a notification that I should continue to wait because prices should fall I can't have any faith that the number of seats I require will be available when they do. This is especially a problem for me because when I fly I am usually purchasing tickets for multiple people.
Given these limitations I find Hopper almost useless for my needs. I would love an app that would allow me to enter a departure date and time window, return date and time window and the number of passengers then provide feedback regarding both future price direction and seat availability. I'm not holding my breath.
I've waited out a week to get cheaper flights to from Japan to NZ.
Still was a rip-off though - one way cost more than a return layover flights to Eastern Europe.
> The Low Fare Forecast (beta) API forecasts whether the lowest published fare will rise, fall or stay the same within the next 7 days.