Facebook Instant Articles. Source: Facebook.

At this year's F8 conference on April 12, Facebook (NASDAQ:FB) will open its Instant Articles format to all web publishers, large and small. The social network rolled out Instant Articles to select publishers last year, enabling them to host content directly on Facebook so it loads faster. After working with publishers over the past few months to fix any issues, Facebook is now ready to roll out the feature to everyone.

That represents a major threat to Google. The Alphabet (NASDAQ:GOOG) (NASDAQ:GOOGL) company generated more than $15 billion from publishers using its advertising products. With Instant Articles, those publishers will more likely use Facebook's own ad solutions. Considering that Facebook drives about a quarter of all Web traffic, Google could find itself losing a large chunk of third-party ad revenue to Facebook.

Fixing Instant Articles
After a few months of testing Instant Articles, publishers weren't happy with their results. While the faster load times may have resulted in more pageviews, publishers were perturbed by the strict advertising restrictions in the format. Those restrictions prevented publishers from generating as much ad revenue per article as on their own websites using different ad solutions like Google's AdSense.

In December, the company relaxed rules dictating the frequency and type of advertising allowed in Instant Articles. It also expanded the feature, so Instant Articles showed up in more users' Facebook apps. The Wall Street Journal reported that those changes helped bring revenue per page view for Instant Articles on par with publishers' own websites.

With those fixes in place, Facebook is ready to expand to smaller publishers, and that's where the real potential to steal revenue from Google is.

Smaller publishers on Instant Articles
Facebook keeps 30% of advertising revenue it fills on Instant Articles, a bit less than the percentage Google keeps from AdSense ads. If a publisher fills its own ad inventory, however, Facebook doesn't make any money, despite spending money to host the content on its servers. Smaller publishers are more likely to opt for the revenue split ads as they lack the resources to fill their own ad inventory.

That means the real money is in the long tail of publishers that don't necessarily draw a lot of traffic individually, but collectively make up a huge chunk of Web traffic. That's where Google makes most of its $15 billion a year from Google Network partners.

Making it easy and worthwhile for small publishers to use Instant Articles should be at the top of the list when Facebook unveils its expansion plans at F8 in April. Investors should pay attention to features aimed at small publishers, especially those that use Google for their current monetization, but drive lots of traffic from Facebook.

Facebook's other efforts to take on Google
While Instant Articles represents a big opportunity for Facebook to take advertising share, it's not putting all its eggs in that basket. Facebook also recently extended its Audience Network to mobile web pages. That means any publisher will be able to display Facebook ads on their mobile sites, taking advantage of Facebook's targeting capabilities.

The Facebook Audience Network was previously limited to other publisher's apps, and in a bit over a year after launching it reached a $1 billion annual run rate. Extending to mobile web activity means Facebook can now make money on the time spent outside of apps on mobile, an area dominated by Google. While that market isn't as large as in-app advertising, Facebook's targeting capabilities and unique ad formats could help expand the market significantly as it takes share from competitors.

So, even if a publisher opts to forego Instant Articles, it may use Facebook to fill its ad inventory anyway. With more web traffic shifting to mobile, Facebook is poised to take further share of the market from Google.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.