Twitter’s user base isn’t growing, at least not significantly, and now the company is ready to hang its hat on a grand theory it has been pitching for more than a year: That it can make money from the millions of people who consume Twitter content but don’t actually have Twitter accounts.

Twitter boasts 320 million monthly active users, but it said last week, for example, that its content reaches one billion people per month. This discrepancy matters for one simple reason: Revenue. The larger Twitter’s audience, the more ads it can sell.

For nearly 18 months, the idea that Twitter could make money off these logged-out content consumers has been presented as a potential revenue stream. Now it’s about to be tested for real.

One of the nuggets from Twitter’s Q3 earnings call Tuesday was a brief mention by COO and revenue chief Adam Bain that Twitter plans to start monetizing its logged-out user base on Twitter as part of a new pilot program sometime this quarter.

“We also are monetizing logged-out users across the network,” Bain said, referring to ads Twitter sells on third-party apps through services like MoPub. “This is the first time that we’ve been doing that. It’s going to come in handy as we also begin to run a pilot here in Q4 for on-Twitter logged out monetization. So we’re going to take some of those learnings and apply it back to Twitter logged-out products.”

Translation: Beginning with this quarter, Twitter plans to show ads to people who visit Twitter.com and user or topic timelines even if they don’t have a Twitter account. That means that if you visit Twitter’s homepage or click on a tweet in a Google search result and find yourself on a user’s timeline, you may also see promoted tweets (a.k.a. advertisements).

The company has said in the past that 500 million people see tweets on Twitter properties each month without logging into an account. Right now, the company isn’t making any money from those people.

But making money from those people is a key way to buoy Twitter’s business. It has become clear that Twitter can’t grow its core user base, at least not with the products it is currently offering. It recently rolled out Moments to entice new users by helping them find event-specific content, like tweets about the World Series, but that alone is unlikely to make a serious dent in Twitter’s user numbers. So if it’s not adding new users, it needs to show Wall Street it can make money from its existing audience instead. This is one way to do that.

Twitter also shows promoted tweets on a few publishing partners like Flipboard, but that test, which has been ongoing for eight months, hasn’t expanded much at all. This is something Twitter can do without relying on a publishing partner.

It is unlikely this pilot will have any immediate effects. For starters, it’s just that — a pilot — which means it will probably be rolled out slowly. It’s likely these ads are also cheaper than the ones Twitter can show its logged-in user base. It simply doesn’t know as much about non-logged-in visitors, which limits its targeting capabilities.

But 500 million people is still a massive group — big enough to make serious waves with Wall Street at some point down the road. For now, though, Twitter is still trying to prove it can turn potential into reality.