Government lawyers made their case in closing arguments of a lawsuit focused on Google's ad tech "stack" -- the suite of tools that website publishers use to sell ads and advertisers use to buy them.

This marks a second major antitrust test for Google this year.

In September, a judge rejected a similar Department of Justice demand to break up the California-based tech giant's world-dominating search engine business.

These cases are part of a broader US government effort to curtail the competitive dominance of big tech companies, including Apple, Amazon and Meta.

Results have been mixed so far -- another judge decided against government lawyers in a suit against Meta's social media empire earlier this week.

In a brief filed ahead of Friday's arguments, the DOJ and multiple US states accused Google of illegally acquiring monopolies in two interconnected advertising technology markets through a "decade-long campaign of ever-mutating unlawful conduct."

The government's case portrays Google as simultaneously controlling multiple sides of the digital advertising marketplace -- owning the platform that publishers use to sell ads, the exchange where transactions occur, and commanding huge advertiser demand.

According to the DOJ, Google once compared this arrangement to Goldman Sachs owning the New York Stock Exchange.

"We are here to fix the problem. We will argue that the best solution is to break up Google's monopoly, which will create a new competitor," Assistant Attorney General Gail Slater said in a post on X.

Google has pushed back, characterizing the proposed remedies as extreme government overreach that would harm publishers, advertisers and consumers.

The company argues its integrated advertising tools deliver efficiency and innovation and that splitting up the service would be technically unfeasible.

The closing arguments follow a liability ruling earlier this year in which Federal Judge Leonie Brinkema found that Google willfully monopolized both the publisher ad server and ad exchange markets.

Prosecutors are seeking sweeping remedies, including forcing the sale of Google's AdX ad exchange and requiring the company to open-source critical auction technology.

According to Laurel Kilgour of the American Economic Liberties Project, Brinkema expressed worry that her remedy decision risked having to be undone, with Google almost certain to appeal, potentially dragging out the process for years.

The closing arguments capped a remedies trial featuring testimony from 19 witnesses and seven experts over 11 days.

The judge in the search case cited the emergence of AI as a reason for treading lightly against Google.

In the ad tech case, DOJ lawyers argue the opposite -- that artificial intelligence advances will likely entrench rather than challenge Google's dominance.

A final ruling is expected in the coming months.

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