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Facebook has made a lot of money selling app install ads in the last few years. Now Google is, too.

Google says developers have generated three billion installs for their apps using Google’s ads, up from two billion in May. That is: Google’s ads have generated one billion installs in four months.

That’s a significant increase in a short period, which is what Google wants us to say when it releases a momentum stat like this. But it’s true!

It’s also true that in May, Google increased the size of its potential market significantly: It started letting advertisers use its “universal app campaign,” which places app install ads on Apple’s iOS devices.

So we may not see the same kind of spike in another four months.

In April, Facebook announced that it had reached the two billion app install mark.

The nice thing for both Facebook and Google is that even if the app boom is over and people are less interested in downloading apps, that doesn’t slow down the market for app ads.

In fact, you could argue that the glut of apps + app fatigue is good for their business, since developers need to work even harder to show off their apps and convince people to use them.