Reach, frequency and GRPs aren't going away. But on their own, they no longer answer the question advertisers actually want answered: did your inventory move the needle?
Why delivery metrics are no longer enough
Delivery is necessary, but it's not sufficient. It tells you what was bought. It doesn't tell you whether the people on the other side did anything new.
What advertisers increasingly want to see
Incremental audience contribution. Search and commerce response by exposure cohort. App engagement after exposure. The numbers that justify a renewal — not just the numbers that justify a slot.