There is a "lowest price guarantee" on Google flights now, wherein they will reimburse you the difference if the flight goes lower in price than if you buy it at that time (through their platform / booking, at least).

To me, this is a signal that Google has used all of its price history data for flights to say "this is a bottom in price", and given they don't want to lose money hand over fist from mispredictions, they're probably right.

I usually set up a price watch on a specific flight I want, then every time it drops, I check if it got the "low price guarantee" stamp of approval and buy then. Even if I'm wrong, I'll get paid the difference either way!