Background: how we got here
The United States v. Google ad‑tech case centres on claims that Google abused its dominance in the open‑web display advertising stack. In April 2025 U.S. District Judge Leonie Brinkema ruled that Google illegally monopolised two markets—the publisher ad‑server market and the ad‑exchange market—and tied those products togetherdigiday.com. Publishers testified that they could not feasibly switch away from Google’s ad‑tech stack because they needed access to Google’s advertising demand, even when Google introduced features they disliked or when alternatives existedreuters.com. The ruling followed a 15‑day liability trial in September 2024 and paved the way for a remedies trial (September–October 2025) to determine how to unwind Google’s illegal monopoly. The remedies debate has broad implications for competition across the digital‑advertising ecosystem and for the publishers, advertisers and ad‑tech providers that depend on it.
The markets at issue
Google’s ad‑tech stack includes:
- AdX – an ad exchange that conducts auctions matching advertiser bids with publisher ad inventory. Professor Robin Lee testified that 60 % of AdX auctions had no competition and that, in those auctions, AdWords was the only bidder in more than half the casesdigiday.com. AdWords (Google’s advertiser network) accounted for 46 % of all indirect open‑web display advertising spend, while Google’s DSP DV360 accounted for another 21 %digiday.com, demonstrating how the buy side is interwoven with the exchange.
- DFP / Google Ad Manager (GAM) – a publisher ad server used to manage ad placements and pricing. Google provides it for free but ties it to AdX; Judge Brinkema found that the tie gave AdX privileged access and deterred publishers from switchingdigiday.com.
Remedy proposals
DOJ’s structural remedy: divestiture + transparency
The Department of Justice (DOJ) argues that Google’s unlawful monopoly can only be remedied through structural separation. Its primary proposal is to divest AdX (and potentially DFP as a contingent step) and open‑source the “Final Auction Logic”—the code governing how bids are ranked and which advertiser winsdigiday.com. Because DFP and AdX are tightly integrated, the DOJ believes that removing AdX will diminish DFP’s dominance naturallydigiday.com. Key elements of the DOJ remedy include:
- Divestiture of AdX: The DOJ seeks to force Google to spin off its ad‑exchange business. Assistant Attorney General Julia Tarver Wood told Judge Brinkema that leaving AdX with Google would give the company “the motive and the means to recreate that tie”reuters.com.
- Open‑sourcing auction logic: Making the final‑auction algorithm public would allow publishers and rivals to verify that auctions are run fairly and would foster interoperabilitydigiday.com. Publishers such as Daily Mail’s Matthew Wheatland and AWS executive Stephanie Layser testified that Google’s auction logic is currently a black box and that only open‑sourcing would end self‑preferencingdigiday.com.
- Contingent DFP spin‑off: The DOJ proposes a phased approach: if divesting AdX and open‑sourcing the logic fail to restore competition, the court could later require the spin‑off of DFPadexchanger.com.
- Escrow fund: Recognising that switching ad servers is costly, the DOJ proposes that Google deposit 50 % of net revenues from AdX and GAM into an escrow fund to reimburse publishers for migration and transition costsdigiday.com. Digital Content Next CEO Jason Kint described the fund as vital to help publishers invest in journalism while the ad‑tech transition unfoldsdigiday.com.
Google’s behavioural remedy: interoperability + restrictions
Google rejects divestiture as “radical and reckless”reuters.com and instead proposes behavioural remedies. Its plan centres on allowing limited interoperability while keeping its tools under one roof:
- Deeper interoperability: Google proposes technical integrations so that publishers using rival ad servers can receive AdX bids in real time. It promises to build an integration with the Prebid header‑bidding framework and to allow publishers to insert Prebid between DFP and AdXdigiday.com. These integrations, however, apply only to open‑web display ads and exclude video, connected‑TV (CTV) and other formatsadexchanger.com.
- Deprecating unified pricing and auction advantages: Google would drop its first‑look/last‑look auction advantages and end unified pricing rules for open‑web display inventorydigiday.com. The company also pledges not to introduce latency or reduce the information provided to publishers, regardless of the ad server they useadexchanger.com.
- Data portability and support: Google promises “reasonable support” to rival ad servers and Prebid servers to ensure publishers can retain their data during migrationadexchanger.com.
Google argues that divestiture would be technically complex and unnecessary. Its counsel insists that the DOJ is “ignoring Google’s legitimate business decisions” and that the online advertising market remains competitivereuters.com. Internal documents that emerged during trial, however, revealed Project Sunday, Google’s own analysis showing that separation of AdX and DFP is technically feasiblemarketingbrew.com. Computer‑science expert Jon Weissman testified that Google’s architecture uses separation‑of‑concerns principles that would support a splitmarketingbrew.com.
What the judge heard
During the remedies trial, Judge Brinkema pressed witnesses on the costs and feasibility of each plan. Testimony highlighted the following perspectives:
- Publishers: Many publishers support structural separation. Advance Local’s Grant Whitmore argued that the DOJ’s proposed breakup would be less disruptive than Google claims, because the burden would fall on Google and the new owner rather than on publishersdigiday.com. Stephanie Layser testified that behavioural remedies would leave too much “wiggle room” and that open‑sourcing auction logic is necessarydigiday.com. Only one publisher witness—WikiHow CEO Elizabeth Douglas—expressed ambivalence, noting that AdX is reliable but acknowledging that publishers fear disrupting existing systemsdigiday.com. Digiday reported that many publishers worry any remedy will arrive too late; the rise of AI search summaries has already caused 30–40 % drops in search traffic and ad inventorydigiday.com.
- Rival exchanges: CEOs from PubMatic, Index Exchange and Kevel testified that Google’s ownership of both the ad exchange and ad server distorts competitiondigiday.com. They emphasised that AdX and DFP must be divested together for interoperability to work and revealed that they had discussed bidding for AdXdigiday.com.
- Advertisers and agencies: Executives from Omnicom, The Trade Desk and others said that Google’s dominance boxes them in; they rely on Google to access must‑have inventory and have little leverage to demand transparencydigiday.com. They support forcing AdX to compete on neutral ground but worry about operational disruption.
- Google and its experts: Google’s witnesses insisted that the stack works efficiently and that pulling it apart would harm competitiondigiday.com. Yet internal documents showed that Google had previously considered spinning off the exchange and server, undermining claims of infeasibilitydigiday.com.
- Expert economists: Harvard economist Robin Lee testified that 89 % of AdWords display ad dollars flowed through Google’s exchange in 2022, compared with 63 % of DV360 spend and only 34 % of budgets from other buying platformsdigiday.com. He also calculated that 66 % of the top 100 publishers using Google’s ad server already use ten or more exchangesdigiday.com—suggesting that publishers can manage multiple partners when incentives align.
- Judge’s concerns: Judge Brinkema questioned whether small publishers could handle the cost and technical work of switching ad serversadexchanger.com. She also raised whether Google might retaliate (e.g., directing its buy‑side to walled gardens) and asked whether strong behavioural rules could sufficeadexchanger.com.
Impact on competition across key verticals
The remedy chosen will ripple through different segments of the advertising ecosystem. Below are the likely effects in major verticals.
1. Publishers and media companies
| Impact area | Structural remedy (DOJ) | Behavioural remedy (Google) |
|---|---|---|
| Dependency on Google | Divesting AdX and open‑sourcing the auction logic would erode the feedback loop that ties publishers to Googledigiday.com. Publishers could integrate multiple exchanges on equal footing and potentially negotiate better fees. Many publishers believe the split is necessary to regain autonomy and transparencydigiday.com. | Google promises to allow Prebid integrations and deeper interoperability, but only for open‑web display adsdigiday.com. Publishers would still depend on Google for video, CTV and in‑app inventoryadexchanger.com, and Google could still wield unified pricing power in those formats. |
| Switching costs | The DOJ’s escrow fund would reimburse migration costs and support smaller publishersdigiday.com. However, switching ad servers is like “rewiring the engine mid‑flight”; it is costly and disruptivedigiday.com. | Google’s behavioural remedy avoids forced migration, appealing to small publishers who fear the disruption. Yet, without structural change, the incentives that discouraged switching remainadexchanger.com. |
| Revenue and pricing | More competition among exchanges could reduce Google’s take‑rate (currently ~20 %)reuters.com, increasing revenue share for publishers. The escrow funds may provide capital for investment in journalismdigiday.com. | Google maintains its integrated platform and could continue to set pricing rules (except for open‑web display). Publishers might see limited improvement in take‑rates and still struggle with opaque auction dynamicsdigiday.com. |
| Transparency and data access | Open‑sourcing auction logic and untying AdX would enable publishers to audit auction outcomesdigiday.com. Data portability would be mandated by court order. | Google offers to provide “reasonable support” and some data export featuresadexchanger.com, but trust in Google’s self‑policing is lowadexchanger.com. |
2. Advertisers and agencies
- Auction fairness and pricing – A divested exchange with transparent logic could level the playing field for advertisers. Professor Lee’s testimony that many AdX auctions had only Google’s own bidder presentdigiday.com suggests that advertisers sometimes overpay due to lack of competition. Structural remedies could force Google’s buy‑side and sell‑side to compete in a neutral auction, potentially lowering advertiser costs.
- Supply access – Behavioral remedies would allow advertisers continued frictionless access to Google’s inventory, preserving efficiency. A structural remedy might introduce friction if the new exchange owner cannot match Google’s scale or reliability, though rivals argue that integration via Prebid could ease transitionsdigiday.com. Advertisers worry about disruptions to campaign execution and measurementdigiday.com.
- Innovation and targeting – More competition could spur innovation in data sharing and contextual targeting. However, advertisers could face fragmentation if multiple exchanges adopt different protocols. Google contends that breaking its stack would slow product innovation and hinder cross‑channel measurementreuters.com.
3. Rival ad‑tech platforms and emerging competitors
- Market entry – Divestiture would create a major new independent exchange (or enable rivals to purchase AdX), opening opportunities for Supply‑Side Platforms (SSPs) and independent ad servers. Testimony from PubMatic, Index Exchange and Kevel underscored their willingness to bid for AdX and the need for fair interoperabilitydigiday.com. Behavioral remedies would still leave Google controlling the largest exchange and server, limiting room for rivals.
- Technical standards – Open‑source auction logic could become a new industry standard. Platforms like Prebid could expand beyond header bidding to unify auctions across formats. Google’s proposal to limit interoperability to open‑web display ads means that other growing areas (video/CTV, in‑app ads, retail media) would remain closed and dominated by walled‑garden platformsadexchanger.com.
4. Consumers and the broader digital ecosystem
- Content diversity – A healthier advertising marketplace could divert more revenue to publishers, supporting local news and diverse content. Publishers fear that, without structural change, Google will continue siphoning value away and that any remedy may come too late given AI‑generated search summaries that are already reducing click‑through ratesdigiday.com.
- Ad quality and privacy – Increased competition may push ad‑tech firms to offer better privacy controls and limit cross‑site tracking. However, if fragmentation leads to more intermediaries, data flows could become more complex. Behavioural remedies rely on Google’s adherence to court‑imposed restrictions, and past mistrust of Google could undermine confidenceadexchanger.com.
Strategic scenarios and outlook
Observers expect Judge Brinkema to issue a remedies decision sometime in 2026; closing briefs and revised proposed final judgements were due on November 3, 2025 and closing arguments are scheduled for November 17, 2025usvgoogleads.com. Court watchers note that the judge appears cautious about imposing a remedy that imposes high switching costs on small publishers but is equally wary of trusting Google to police itselfadexchanger.com. Many expect her to combine behavioural and structural remedies—for example, mandating interoperability, banning self‑preferencing and first/last look practices, appointing an external monitor, and keeping divestiture of AdX (or DFP) in reservedigiday.com.
Possible outcomes
- Full structural remedy: The court orders divestiture of AdX and open‑sourcing of auction logic, with DFP spin‑off contingent on performance. This scenario could foster competition, encourage innovation in independent ad exchanges and servers, and reduce Google’s share of open‑web display advertising. Publishers would benefit from increased transparency and potentially higher revenue shares, while rival SSPs and ad‑servers could gain significant market share. The escrow fund would cushion the transition, though small publishers would still face temporary disruption and the new exchange owner would need to maintain scale and reliability.
- Behavioural remedy with strong monitoring: The court adopts Google’s interoperability commitments but strengthens them: requiring Prebid integration across all formats (including video/CTV), banning first/last look across the board, and appointing a monitor to oversee compliance. This would leave Google’s stack intact but impose guardrails. Competition would improve modestly, though critics worry that without structural change Google’s incentives will remain misaligned and that the company could circumvent rulesadexchanger.com.
- Hybrid remedy: The court imposes behavioural remedies immediately and sets a timetable for potential divestiture if competition fails to materialise (e.g., revisit in two years). This approach would give Google an opportunity to demonstrate good faith while holding structural separation as a real threat. Publishers might view this as too slow, but it reflects the judge’s cautious approachadexchanger.com.
Conclusion: stakes beyond the courtroom
The remedies phase of U.S. v. Google is more than a technical antitrust dispute—it will shape the competitive landscape of digital advertising for years to come. The case exposes how the integration of an ad exchange, ad server and buy‑side tools can create information asymmetries and self‑preferencing that disadvantage publishers and advertisers. Structural separation offers the promise of a more open and transparent marketplace, while behavioural remedies test whether robust rules and monitoring can rein in a powerful platform without breaking it apart. Whatever remedy Judge Brinkema chooses, the decision will set a precedent for how courts and regulators address digital‑platform monopolies. It could also influence ongoing antitrust actions against Meta, Amazon, Apple and other tech giantsreuters.com.
One point is clear: the open web’s future depends on a functioning, competitive ad‑tech ecosystem. Whether through structural change, strict behavioural rules or a hybrid approach, the outcome will determine whether publishers can continue to fund journalism, whether advertisers can access diverse audiences at fair prices, and whether rival ad‑tech firms can innovate. As the digital advertising industry braces for the court’s decision, the hope is that whatever comes next will restore competition and ensure that the open web remains a viable marketplace for content, commerce and innovation.
