Antitrust Grows Up

For most of the last two generations, American antitrust law ran on a single diagnostic test. If a merger or a business practice made consumer prices go up, it was suspect. If prices stayed flat or fell, the conduct was presumptively fine, whatever else it did to rivals, workers, or the shape of a market. This was the consumer-welfare standard, and it had the virtue of being measurable: an economist could put a number on it, a judge could apply it, and a company’s lawyers could plan around it years in advance. It also had a blind spot roughly the size of the modern digital economy, where the most consequential products are given away free and the harm shows up not in a receipt but in what disappears from the shelf, the feed, or the labor market. The current wave of cases against large platform companies is best understood as enforcers trying to patch that blind spot without a legal architecture built to hold the patch in place.

From price effects to structure

The doctrinal shift is real, and it did not start with the current administration. The intellectual groundwork goes back to law review arguments from the mid-2010s that a price-only framework simply could not evaluate a firm that subsidizes one side of a market to extract rents from the other, or that uses a dominant position in one layer of the stack to foreclose competition in an adjacent one. What changed over the following decade is that this critique moved from academic sympathy to prosecutorial practice. Cases brought against search, app-store, and ad-tech businesses have leaned less on “did this raise the price consumers pay” and more on structural questions: does the firm control both sides of a transaction and referee its own participation in it, does it own the pipes and compete with the traffic running through them, and can it use data or default positions accumulated in one product to entrench dominance in another. The remedies sought have moved in parallel — not fines calibrated to overcharge, which is the traditional currency of price-based cases, but divestitures, mandated interoperability, and in the more aggressive filings, outright separation of a business line from the parent.

That is a genuinely different theory of harm, and it is worth being precise about why it emerged where it did. Advertising technology is the clearest illustration. A firm that operates the tool publishers use to sell inventory, the tool advertisers use to buy it, and the exchange that clears the trade between them is not merely a large player — it is positioned to set the terms of a market it also participates in, in ways that a price-effects test is not well equipped to see, because the distortion shows up as fee structure and auction mechanics rather than list price. Regulators concluded, reasonably, that policing conduct like this piecemeal — one settlement over auction rigging, another over self-preferencing — could not keep pace with how quickly the underlying architecture could be reconstituted. Structural separation was the response: if the conflict of interest is inherent to owning all three legs of the stool, take away one of the legs.

The doctrinal question courts are now wrestling with is not whether platform power is real, but whether the remedy for it fits inside the antitrust statute at all.

What the platform cases actually signal

For platform businesses more broadly, the signal is not “get bigger, expect a breakup.” It is narrower and, for compliance planning, more useful: exposure now scales with the number of distinct competitive roles a company occupies inside a single value chain, not simply with market share in any one of them. A company that is a large marketplace and nothing else looks less exposed under this framework than a company that is a smaller marketplace, the analytics vendor to sellers on that marketplace, and a preferred buyer in the same market — even if the second company has less raw market power by any conventional share metric. This is a break from the merger-guidelines logic that dominated the 1980s through the 2000s, where horizontal share was the master variable. It rewards companies for staying in their lane and penalizes vertical integration in ways that will surprise executives who built their moat on exactly that integration, because for a long stretch of the consumer-welfare era, owning more of the stack was the textbook way to lower costs and therefore prices — precisely the thing the old test rewarded.

It also changes how these cases get litigated, because structural remedies invite a different kind of defense. Under a price-effects regime, a defendant’s best argument is usually empirical: show the econometrics, show that output rose and prices fell. Under a structural theory, the defense shifts to a design argument — that the conflict the government describes as inherent is actually manageable through firewalls, information barriers, or contractual commitments short of divestiture. Expect to see a lot more of that argument in the next few years, because it is the one most likely to find a sympathetic judge, for reasons that get to the second half of this story.

The gap between ambition and what courts will uphold

Here is the tension nobody entirely wants to say out loud: American antitrust statutes were not written with structural break-up as their default remedy, and the courts asked to bless these newer theories are, by composition and training, more comfortable with the price-effects framework than with the market-architecture one. A judge asked to order a divestiture has to be persuaded not just that a conflict of interest exists, but that severing a business line is a proportionate response under the specific remedial powers Congress granted — a much higher bar than finding liability in the first place. The historical base rate for successful structural relief in monopolization cases, outside of the handful of landmark examples usually cited precisely because they are exceptional, is thin. Courts have repeatedly shown they will find conduct unlawful while declining to order the remedy the government actually wants, opting instead for behavioral commitments — the firewalls and reporting obligations the defense bar prefers — because those are easier to write into a consent decree and easier for a court to supervise without effectively running a company.

That gap between enforcement ambition and judicial appetite is where this era of antitrust will actually be decided, and it cuts against tidy narratives on both sides. It is not simply that regulators are overreaching against a hostile judiciary, nor that courts are captured apologists for concentrated power. It is that structural theories of harm are conceptually sound responses to a real problem — markets where a single firm plays several conflicting roles at once — while remaining underdeveloped as litigated law, tested in only a handful of full trials rather than settled by consent decree. Every case that goes the distance rather than settling adds real precedent in either direction, and the appellate courts hearing the current cohort of appeals will do more to define enforceable antitrust doctrine for the next decade than any settlement, however large the headline penalty. The prices question, in other words, has not disappeared. It has simply stopped being the only question that matters, and the law is still working out how to ask the others without the answer collapsing back to the one test everyone already knows how to grade.