Behind a secret deal between Google and Facebook

In 2017, Facebook said it was testing a new way of selling online advertising that would threaten Google’s control of the digital ad market. But less than two years later, Facebook did an about-face and said it was joining an alliance of companies backing a similar effort by Google.

Facebook never said why it pulled back from its project, but evidence presented in an antitrust lawsuit filed by 10 state attorneys general last month indicates that Google had extended to Facebook, its closest rival for digital advertising dollars, a sweetheart deal to be a partner.

Details of the agreement, based on documents the Texas attorney general’s office said it had uncovered as part of the multistate suit, were redacted in the complaint filed in federal court in Texas last month. But they were not hidden in a draft version of the complaint reviewed by The New York Times.