Meta Platforms is confronting one of the most consequential legal challenges in its history as a landmark federal trial examines whether Facebook and Instagram were deliberately designed to keep young users engaged at the expense of their safety.

The case, brought by a coalition of 29 U.S. states, began this week in federal court in Oakland, California. Four lead states — California, Colorado, Kentucky and New Jersey — accuse Meta of designing its platforms to “hook” children and teenagers, misleading the public about the risks and improperly collecting data from children under 13.

The trial could last roughly six weeks and has implications that extend far beyond the financial penalties being sought.

At stake is the way Meta designs its products, how recommendation algorithms are used and whether an engagement-based social-media business can remain largely free from liability for the consequences of its product decisions.

The states' central argument is that Meta's platforms were not simply popular products that happened to attract young people.

Prosecutors contend that Meta deliberately built systems designed to maximize engagement and retain younger users because greater attention creates more advertising opportunities and more valuable behavioral data.

California Deputy Attorney General Megan O'Neill described the alleged strategy in court as an effort to attract users, keep them engaged and monetize their activity.

The states also point to internal communications and company research as evidence that Meta understood the risks of its products.

Former Meta engineer Arturo Bejar, the first witness for the states, testified that internal monitoring focused heavily on violations of content policies rather than measuring the actual harm experienced by young users.

Meta's defense has presented a very different interpretation.

The company acknowledges that some young people can struggle with social-media use but argues that research has not established a clear causal connection between ordinary use of its platforms and declining adolescent well-being.

Meta's attorneys also say the company has continuously worked to improve safety and that private language used by individual employees should not be confused with company policy.

The distinction is important.

The legal question is not simply whether Facebook or Instagram can be harmful to some users.

The states must persuade the court that Meta violated applicable laws by designing or operating the platforms in ways that created legally actionable risks.

Meta has said the penalties could theoretically reach $1.4 trillion under the states' calculations.

The states have suggested a figure closer to $200 billion.

Neither figure represents a judgment that Meta has been ordered to pay, and the court would have to determine liability and any appropriate remedies before imposing penalties.

The financial figure nevertheless illustrates the scale of the dispute.

A sufficiently large penalty could materially affect Meta's capital allocation, even though the company generates enormous annual profits.

But the more important risk may be operational.

The plaintiffs are seeking significant changes to Meta's products.

Among the requested measures are eliminating features such as likes and infinite scrolling, introducing time limits for younger users and enforcing stronger restrictions intended to prevent children under 13 from using the services.

Those proposals strike directly at mechanisms that have helped make the platforms commercially successful.

Infinite scrolling, recommendations and engagement features are not minor interface details.

They are central parts of the systems that determine what users see and how much time they spend on Meta's services.

Any court-ordered redesign could therefore have implications for user engagement and advertising revenue.

Arturo Bejar's evidence is particularly important because he worked inside Meta.

He was involved in surveys examining teenagers' experiences on Instagram and told the court that young people were experiencing harm at unusually high rates.

He said he raised those concerns with company leadership and believed Meta's internal monitoring failed to capture the full extent of the problem.

Meta attempted to block his testimony, citing concerns about deleted communications, but Judge Yvonne Gonzalez Rogers rejected that effort.

His testimony could become a major part of the states' effort to demonstrate that the company knew about potential risks and failed to respond adequately.

Meta's trial is not an isolated event.

The company is facing thousands of lawsuits from states, municipalities, school districts and individual plaintiffs over alleged harms to young users. Other major platforms, including TikTok, Snapchat and YouTube, are facing similar litigation.

Earlier cases have already produced significant consequences for Meta.

A New Mexico case resulted in a $942 million judgment and an order requiring changes to Meta's platforms in the state, according to Reuters. A separate Los Angeles jury awarded $6 million in a case involving alleged social-media addiction.

Those cases do not determine the Oakland outcome, but they demonstrate the growing legal pressure surrounding the industry.

Meta's shares fell 4.4% on the first day of the trial, underscoring how seriously investors are treating the litigation.

The concern is not necessarily that one financial judgment will destroy Meta.

Rather, investors are evaluating the possibility of a broader change in how the company's platforms operate.

If regulators and courts force Meta to reduce engagement-driven features, restrict data collection or impose stronger age controls, the company could face lower engagement, higher compliance costs and potentially weaker advertising economics.

That would create a different risk profile for the business.

The case could also establish an important precedent for other internet platforms.

If Meta is found liable based on product-design decisions rather than individual pieces of harmful content, other social-media companies could face similar challenges.

That would move the legal debate away from whether platforms are responsible for what users post and toward whether companies are responsible for the architecture that encourages users to remain on the platforms.

Such a shift could reshape the technology industry's approach to product development.

The case ultimately raises a fundamental question about the economics of online platforms.

For years, technology companies have optimized products for engagement because user attention has direct commercial value.

The more time people spend scrolling, watching videos and interacting with recommendations, the more opportunities platforms have to display advertising and collect behavioral data.

The states argue that this model becomes unacceptable when companies knowingly apply it to children and teenagers.

Meta insists it can address safety concerns without conceding that its basic products are defective or intentionally harmful.

The six-week trial is therefore a defining moment for Meta and potentially for the wider social-media industry.

If Judge Rogers finds against Meta, the company could face major financial penalties and be forced to redesign fundamental parts of Facebook and Instagram.

If Meta prevails, it would gain an important legal defense against the growing number of youth-safety cases facing the industry.

The trial is still in its early stages, and neither side has established its case.

But the significance is already clear.

Meta is not simply defending its reputation.

It is defending a business model built around maximizing engagement — and the outcome could help determine how much legal responsibility technology companies carry for the way they design products used by millions of young people.