After hearing three hours of closing arguments from both the U.S. Justice Department and Google, the federal judge—who presides over the U.S. District Court for the Eastern District of Virginia—must determine how to remedy what she has already ruled is an illegal monopoly in the online advertising technology market. Her final ruling is expected sometime next year, and whatever she decides could reshape the digital advertising landscape that fuels much of Google’s global business.

The government is asking the court to impose sweeping structural changes, including forcing Google to spin off the technology that manages real-time transactions between advertisers and publishers. This core platform, known as an ad exchange, processes a staggering volume of traffic—an employee testified that Google receives 8.2 million requests to sell ad space every second. The Justice Department also wants the company to disclose certain data and potentially divest additional ad-selling tools if competition fails to improve.

Google has countered with a far narrower plan, arguing that behavioral changes and increased data transparency would be enough to restore competitive conditions without tearing apart the core of its advertising infrastructure.

Judge Brinkema approached Friday’s arguments with only a handful of questions, most of which centered on timing. She expressed concern about whether a breakup would come too late to affect a rapidly evolving industry, especially if Google appeals her earlier ruling. A court-ordered behavioral remedy, she noted, could be implemented immediately.

Her decision carries enormous implications. Google’s advertising arm remains one of the most powerful engines in a business valued at $3.64 trillion, playing a central role in the company’s ability to shape online commerce and information flow. If she orders a breakup, it would mark the first time a modern internet-era tech giant is forced to sell off a major part of its business.

Google narrowly avoided such a fate in a separate antitrust case earlier this year, when a judge declined to order the company to sell its Chrome browser despite finding that Google illegally maintained a monopoly in search. That decision instead required data-sharing and modest operational changes—outcomes widely seen as a win for Google.

Still, many legal experts argue that the advertising technology case presents a more compelling opportunity for regulators to secure a structural remedy. It is part of a much broader government effort to curb the power of dominant tech companies. Although regulators achieved early successes, more recent rulings have been mixed. A judge this week determined that Meta did not illegally suppress competition by acquiring Instagram and WhatsApp, dealing a blow to the government’s campaign.

Other battles continue. Apple is facing claims that it made switching away from its devices unreasonably difficult. Amazon is under scrutiny for allegations that it exploits smaller merchants that rely on its marketplace.

The ad tech case—United States et al. v. Google—was filed in 2023 by the Justice Department and several states. Prosecutors argued that Google controlled every major layer of the process that determines which ads appear on websites. By dominating the tools used by publishers and advertisers and operating the auction system at the center, they said, Google was able to extract an outsized share of revenue.

Judge Brinkema agreed in an April ruling, finding that Google held unlawful monopolies over two segments: the tools used by publishers to sell ad inventory and the software that conducts transactions between publishers and advertisers. She did not find that Google monopolized the tools advertisers use to buy ads.

A two-week hearing in September focused on remedies. Government lawyers insisted that spinning off Google’s exchange platform and opening the code for its publisher tools were necessary steps to restore competition. They argued that if Google were left with any ability to control key systems, it would inevitably find ways to undermine reforms.

Matthew Huppert, representing the Justice Department, warned that partial measures would fail, saying Google would work aggressively to minimize their impact. He urged the court to adopt a structural approach, calling a more competitive future for the open web both possible and urgently needed.

Google’s attorney, Karen Dunn, countered that a breakup would be unprecedented, unnecessary, and unsupported by legal precedent. She argued that transferring the ad exchange to a new owner would take far longer than the government suggested, largely due to the immense volume of customer data that would need to be migrated. By contrast, she said, Google’s proposed changes could be fully implemented within 12 to 15 months.

Throughout the proceedings, Judge Brinkema has signaled openness to both approaches at different times. In May, she questioned whether a divestiture might be the most effective remedy. But during the September hearings, she pressed witnesses on whether strict behavioral oversight might accomplish the same goals with fewer disruptions.

On Friday, she emphasized that the centerpiece of her upcoming decision would be whether a breakup is truly required.

The stakes could not be higher—for Google, for regulators seeking to rein in big tech, and for the broader digital advertising ecosystem that underlies much of today’s online economy. As the judge finalizes her ruling, the industry is bracing for a decision that could redefine the boundaries of corporate power in the internet era.