Retraining models every time a advertiser wins a bid on a keyword is unwieldy. Most likey solution is training the model to emit tokens represent ontological entries that are used by the Ad platform so that "<SODA>" can be bid on by PepsiCo/Coca-Cola under food > beverage > chilled > carbonated. Auction cycles have to match ad campaign durations for quicker price discovery, and more competition among bidders