Google and Meta are quietly rewriting the rules of ad measurement, and they’re doing it with open-source marketing mix modeling (MMM) tools that many marketers don’t even realize they’re using.

MMM is a method for measuring the relative performance of different marketing channels. It fell out of favor because it takes a long time and isn’t deterministic. But since Apple, Google and regulators around the world began cracking down on online tracking, MMM has come roaring back into fashion.

So much so that Google and Meta jumped in with their own open-source MMM tools, called Meridian and Robyn, respectively.

Now, Meridian and Robyn are reshaping the independent measurement ecosystem.

According to numerous agency execs and attribution tech vendors AdExchanger spoke with, Google and Meta have aggressively pushed their MMM tools as a new attribution standard.