Alphabet Inc.’s Google has spent the past week in Virginia federal court seeking to persuade a judge that selling off its advertising exchange is too risky, technologically difficult and would disrupt the market.

Over the past five days, witnesses testifying on Google’s behalf said that a forced sale would upset a business worth $15.9 billion in revenue, according to U.S. estimates for 2025 by research firm Emarketer, create ripples of uncertainty across the market, degrade service for the smallest online publishers and scare away potential buyers.

The trial is focused on how to restore competition to the technology that underpins the display advertising business controlled by Google after Judge Leonie Brinkema ruled in April that the company had an illegal monopoly in two markets — the advertising exchange and publisher-side technology, known as an ad server.

Google also offers ad-buying tools for advertisers in addition to ad-selling ones for website publishers and a trading exchange where both sides complete transactions in lightning-fast auctions.

To remedy the illegal conduct, the Justice Department has proposed that Google be forced to sell off the exchange, AdX, and make public the logic behind how the ad server decides which advertisement to show. If those changes don’t resolve competition issues in the market, the Justice Department has requested that Google also be forced to sell off its ad server over time.

Google has countered with a proposal to integrate its technology with a popular alternative, known as Prebid, as well as with rival ad servers. It’s also pledged not to re-enable certain auction mechanics the court found gave it illegal advantages, known as “first look” and “last look.”

But the company has spent most of its time defending against the Justice Department’s proposal that it be forced to sell off AdX — which according to the agency’s estimates controls about 56% of the market for the display ads that power much of the open web.

Here are Google’s main arguments:

Divestiture is technologically hard

Several Google engineers and outside technical experts hired by the company have testified that untangling AdX from the rest of the company’s technology would be difficult.

Today, the ad exchange, AdX, and the publisher ad server have been integrated into one product called Google Ad Manager. That allows them to share processing capabilities and reduce the amount of time it takes to select and load an ad on a web page, said Glenn Berntson, the engineering director for Google Ad Manager.

About 300 engineers work on the product and it has about 35 million lines of code, he said. While it would be possible to isolate and copy the software code that makes up AdX, Berntson said, the exchange “can’t run without Google’s infrastructure.”

Heather Adkins, Google’s vice president of security engineering, likened the relationship of AdX and Google’s core infrastructure to knitting.

“It’s tightly coupled,” she said, adding that the product is “interdependent once it gets compiled and is running on the infrastructure.”

The Justice Department argues that the links between Google’s AdX product and its core infrastructure could be replaced by tools offered by cloud providers, including the company’s own Google Cloud Platform. While Adkins acknowledged that some of the services within Google’s core have analogs on Google’s cloud, they might not function in the same way.

Jason Nieh, a computer science expert from Columbia University, said Google’s core was custom built for the company’s products and has special features to ensure they work quickly and at scale. He likened the core to legendary basketball player Michael Jordan, saying its high-performance characteristics mean that any commercially available alternatives likely can’t offer the same level of quality. Nieh said that he wasn’t sure it’s feasible to divest AdX if so, it could take a minimum of five years.

Still, Google’s Adkins acknowledged that Alphabet is currently decoupling its life sciences division Verily and transferring it to the Google Cloud Platform. The life sciences platform would operate independently from Alphabet, and be either sold or spun off, Adkins said. The government has pointed to her testimony to show that splitting off a technically complex unit is doable.

Sale introduces many unknowns

Shane Goodwin, a business professor at Southern Methodist University, testified that many of the ambiguities around a potential sale are likely to deter buyers. The court has yet to determine the extent of the assets for sale, and could leave that up to a divestiture trustee, he said. The Justice Department is also maintaining veto rights over the buyer. Because AdX is a global business, a transaction might require competition approval in Europe or elsewhere, adding to the time it would take for a transition, he said.

Goodwin testified that other large tech players, such as Amazon.com Inc. or Meta Platforms Inc., may be ineligible to bid because of antitrust risk, while smaller businesses are unlikely to have the financial capital for a purchase. The operational complexities and time a transition would take are likely to deter financial buyers, like private equity, he said.

Those same “unknowns” plague a potential sale of the ad server, he said, with the added uncertainty potentially leaving the market in limbo for nearly a decade.

In response, the Justice Department pointed to a 2020 presentation by the investment banking firm Lazard Inc. that highlighted several potential buyers including Oracle Corp., Adobe Inc., SAP SE and Salesforce Inc., as well as buyout firms including Centerbridge Partners and GTCR.

Customers would face disruptions

Google witnesses also testified that a sale of AdX would hurt publishers, especially the smallest ones.

Elizabeth Douglas, the chief executive officer of wikiHow, which offers how-to articles, said that firms like hers rely heavily on Google’s advertising products for their revenue and could suffer from the sale.

WikiHow uses Google’s Ad Manager to monetize the content, and Douglas said she worries whether a new AdX owner would offer less support and fewer safeguards against bad ads. About 30% of wikiHow’s revenue comes through AdX, Douglas said, and another 10%-15% from a content licensing agreement with Google.

“Having our ads work the way they do is the stable part of my business right now,” Douglas said, noting the company has declining revenues because of what she called the “AI apocalypse” leading to less traffic for the site. “I want to spend my time saving our business from the problems we are having with AI.”

The smallest businesses today can use Google’s ad server for free. If the ad server were sold, that might no longer be the case, several Google witnesses said.

Justice Department lawyers questioned Douglas about the AI threat, noting that the firm’s licensing deal lets Google use wikiHow’s content to train its own AI, which in turn cannibalizes Douglas’ business. That’s been the case for the whole online publishing industry. Google’s AI-generated answers — and the way it has changed its search algorithm to support them — have caused traffic to independent websites to plummet, Bloomberg previously reported.

Selling off AdX raises security concerns

The data security risks are also an argument Google witnesses focused on. Adkins said that the company’s ad products have extra levels of security because of their relationship with Google’s core infrastructure.

Divesting AdX could make it “a target” for bad actors, she said on Thursday. “It could be of interest to an intelligence agency or a nation state.” Would a new buyer “be able to defend billions of people whose data ends up in the databases?”

A third-party would have to build the equivalent security in a new system because of AdX’s reliance of Google’s core, she said. “It’s a question of time.”

Nirmal Jayaram, a senior director of engineering at Google, said that a divestiture would lead to more spam and ad fraud in the market. Google’s integrated system has signals to detect spam and fraud, which advertisers and publishers both benefit from, he said.

If AdX is sold, “that is lost,” he said.

The Justice Department argued that Google had been hacked before despite the alleged security, pointing at events in 2009 and 2018 that exposed user data.

(With assistance from Davey Alba.)

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