Facebook plans to shut down FBX, the ad exchange that allows advertisers to buy retargeted desktop ads using third-party tools like Criteo and AppNexus.

The news was first reported in The Wall Street Journal and we’ve confirmed it with Facebook. In an emailed statement, Vice President of Monetization Product Marketing Matt Idema suggested that this is part of Facebook’s shift to mobile (in its most recent earnings report, mobile accounted for 82 percent of Facebook’s ad revenue). He said:

Mobile is now a necessary component of effective marketing campaigns, and Facebook is helping millions of businesses understand their customers’ purchase path across devices. Dynamic Ads and Custom Audiences have mobile at their core and are delivering excellent results for businesses, so Facebook Exchange spending has shifted towards those solutions. This is about giving people more relevant ads and marketers more effective formats, especially in an increasingly mobile world. Our ads API is open to all developers so they can innovate on our platform and build great ad experiences for brands and their customers.

Facebook launched FBX back in 2012, but its focus seemed to have shifted away from the exchange in recent years.

Antonio Garcia-Martinez, a former Facebook product manager who helped build FBX (and author of a forthcoming Silicon Valley memoir), likened the move to “Goldman Sachs saying it won’t do high-frequency trading.”

“Whatever happens with FBX, Facebook will have an exchange again at some point, when they’ve lost the leverage needed to maintain a walled garden of clunky ads technology,” Garcia-Martinez wrote. “They’ll just launch it as if FBX never existed, and make it seem like it was part of the plan all along.”

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