A federal trial that experts are calling a defining moment for the social media industry — some have compared it to the legal reckoning once faced by Big Tobacco — opened Tuesday in Oakland, California, as a coalition of 29 US states accused Meta of intentionally engineering Facebook and Instagram to addict children and teenagers. The trial, which is expected to last six weeks, represents the most serious legal challenge Meta has yet faced over the effects of its platforms on young users.

Four lead states — California, Colorado, Kentucky and New Jersey — set out their case in opening arguments, alleging that Meta knowingly designed product features to maximise the time young users spent on its apps, harvested their data, violated federal and state children's privacy laws by collecting data on under-13s without parental consent, and then misled the public about the risks involved. California Deputy Attorney General Megan O'Neill distilled the states' theory of the case into a blunt formula: Meta sought to "hook the users, hold them for as long as they can, harvest their data, and then hide the truth from the public." She drew heavily on Meta's own internal documents — millions of pages of research reports, employee emails and chat logs, some of which reached chief executive Mark Zuckerberg — to argue that the company was privately aware its platforms caused harm while publicly insisting they were safe. One internal research note stated that "teens have an addict's narrative about use"; another acknowledged that "product features designed to increase time spent are inherently at odds with well-being."

Meta's lead attorney, Paul Schmidt, pushed back firmly on the central allegations. He argued that the same internal document cited by the states also found that 41 percent of teens said Instagram made them feel better, and another 41 percent reported no effect — context he said the states had stripped away. Schmidt contended that social media addiction, as a clinical concept, does not exist, and that no clear research link has been established between adolescents' social media use and measurable harm to their well-being. He also argued that the very privacy laws Meta stands accused of violating had, paradoxically, limited the company's ability to collect and retain the data that would have allowed it to identify and remove underage users more effectively. Zuckerberg and Instagram chief Adam Mosseri are both expected to testify during the trial. After opening arguments, former Meta safety engineer Arturo Bejar took the stand as the states' first witness, telling jurors that "move fast and break things" was a guiding philosophy at the company and that safety was often not considered when new products, such as Reels short-form videos, were launched.

Outside the courthouse, parents gathered to protest, some describing personal tragedies they attributed to their children's use of Meta's platforms. One mother described her daughter, who started using Instagram at 12 and died at 17 of a drug overdose, having purchased substances through the platform. Another parent said her 15-year-old son died by suicide in 2021 after being targeted by a predator on Facebook. The states are seeking penalties that could reach as high as $1.4 trillion — a figure close to Meta's total market value, though attorneys general have suggested a more realistic target of around $200 billion, roughly three years of after-tax profit. They are also demanding structural changes to both platforms, including the elimination of infinite scroll and "like" counts, the introduction of time limits for younger users, and stricter enforcement of the existing ban on under-13s.

The trial arrives at a moment of mounting legal pressure on the broader social media industry. Snap, TikTok parent ByteDance and YouTube parent Alphabet all face thousands of related lawsuits from states, school districts and individuals. Earlier this year, a Los Angeles jury ordered Meta and Google to pay $6 million to a young woman who said she became addicted to Instagram and YouTube as a child; a New Mexico judge separately ordered Meta to pay $567 million over teenagers' mental health. Stanford law professor Nora Freeman Engstrom has described the current case as potentially "the beginning of a broader reckoning" for Meta, warning that a loss could force the company to fundamentally overhaul two of the world's most widely used platforms. The trial's outcome will be determined not by the jury — whose role is advisory — but by US District Judge Yvonne Gonzalez Rogers.