Meta Platforms is facing one of the most consequential legal battles in its history as a major federal trial begins in California over allegations that Facebook and Instagram were deliberately designed to encourage addictive use among children and teenagers.

The case, brought by a coalition of 29 U.S. states, opened Tuesday in federal court in Oakland. Four states — California, Colorado, Kentucky and New Jersey — are leading the consumer-protection claims at trial, while the broader coalition has also accused Meta of violating federal children's privacy law.

The litigation could result in enormous financial penalties, but the potential business consequences may be even more significant.

The states are seeking changes to some of the core features that helped make Meta's platforms highly engaging, including recommendation systems, infinite scrolling and other mechanisms designed to keep users returning.

The allegations go beyond the familiar question of whether young people encounter harmful material online.

The states argue that Meta made deliberate product-design choices that encouraged compulsive use and exploited vulnerabilities among younger users.

They also allege that the company misled the public about the safety of its platforms and improperly collected data from children under 13 without parental consent.

Meta rejects those claims.

The company says it has invested heavily in youth safety and argues that the states have not established that Facebook and Instagram were intentionally designed to cause the alleged harms.

The case is therefore fundamentally about corporate responsibility.

At what point does a technology platform's design become legally responsible for the way users interact with it?

Meta has disclosed that the four states leading the consumer-protection case could seek as much as $1.4 trillion in penalties if the company loses.

The figure is extraordinary, roughly comparable to Meta's market value at the time it was disclosed. Meta has argued that such a penalty would be unprecedented.

But the $1.4 trillion number should be viewed as a potential maximum rather than an expected judgment.

The actual financial outcome would depend on the court's findings and the legal formula used to calculate any penalties.

The states' broader strategy is arguably more important than the headline number.

They want changes to how Meta's products operate.

Among the potential remedies are restrictions on engagement-driven features and stronger age verification.

The states have pushed for measures involving infinite scrolling, algorithmic recommendations and other features that can encourage users to spend more time on the platforms.

If the court ultimately orders such changes, the impact could extend directly to Meta's business model.

Facebook and Instagram generate advertising revenue partly through user engagement.

Changes that reduce time spent on the platforms could affect the amount of advertising inventory available and potentially change how the company designs its recommendation systems.

That is why this case is more significant to investors than a conventional damages lawsuit.

The trial has an unusual structure.

Judge Yvonne Gonzalez Rogers selected an eight-person advisory jury, consisting of five women and three men. The jury's eventual findings will not be legally binding; the judge will make the final decision.

The arrangement is unusual because most high-profile civil trials use juries whose verdicts directly determine factual findings.

Here, the advisory jury will essentially provide the judge with a community perspective while allowing her to retain final control.

The proceedings are expected to last roughly six weeks.

One of the most closely watched parts of the case will be evidence from Meta's own internal research.

The states are expected to argue that company employees and researchers knew that certain platform features could pose risks to teenagers while the company publicly presented the products as safer.

That type of internal evidence has been critical in previous cases against large technology companies.

Meta will likely argue that research about possible risks is not equivalent to proving deliberate misconduct and that the company has continuously changed its products in response to emerging evidence.

Meta enters the trial with a mixed but increasingly difficult legal record.

The company has already faced other lawsuits alleging that its platforms contribute to youth harm.

In New Mexico, a court found Meta liable in a separate case involving allegations concerning the safety of its platforms and imposed significant financial penalties. Reuters and other reports have also documented additional lawsuits from families, school districts and state governments.

A separate Los Angeles case previously produced a verdict against Meta and Google in litigation over social-media addiction claims.

Those cases do not determine the outcome of the Oakland trial, but they demonstrate that Meta is facing a broad legal campaign rather than an isolated lawsuit.

Supporters of the states' legal strategy increasingly compare the social-media litigation to earlier campaigns against industries accused of causing widespread harm.

The analogy is attractive because the lawsuits seek both financial consequences and changes to corporate behavior.

Critics, however, argue that social media is fundamentally different from tobacco or other products because platforms have legitimate social and communication benefits and because scientific evidence about the precise causes of youth mental-health problems is complex.

That distinction could become an important part of the trial.

Meta's financial position means that even a very large penalty would not necessarily threaten the company's survival.

The bigger risk could be precedent.

If the court establishes that certain engagement-focused design practices violate consumer-protection laws, other states and private plaintiffs could use the ruling to pursue similar claims.

The company could then face years of additional litigation and pressure to modify its platforms.

That would raise costs and potentially constrain product development.

It could also affect other social-media companies.

TikTok, Snap and YouTube are facing related claims over youth safety and platform design, meaning a major ruling against Meta could have consequences throughout the industry.

The Oakland trial is ultimately about more than Instagram or Facebook.

It is a test of whether technology companies can be held responsible for designing products that maximize attention, particularly when those products are used extensively by children.

If the states prevail, the case could accelerate a shift away from engagement at any cost and toward stronger design obligations for minors.

If Meta wins, the company would gain a major legal defense against a growing wave of lawsuits and regulatory claims.

Either outcome could become a landmark for the technology industry.

For Meta, the stakes are enormous: potential financial liability, product restrictions and a precedent that could reshape how billions of users interact with its platforms.

For regulators, parents and other technology companies, the case could help establish where the legal boundary lies between a highly engaging product and one that the law considers dangerously addictive.

As opening arguments begin, Meta is not merely defending Facebook and Instagram.

It is defending a central model of the modern internet — one in which maximizing user attention has long been one of the most valuable assets a technology company can possess.