Meta CEO Mark Zuckerberg took the stand Wednesday in Los Angeles Superior Court in a landmark trial over claims that social media platforms harm children, marking his first time answering youth safety allegations before a jury.

The bellwether lawsuit, K.G.M. v. Meta Platforms, Inc., et al., was filed by a 20-year-old California woman identified by her initials. She alleges that Meta and other social media companies engineered their platforms to hook young users, fueling her depression and suicidal thoughts, and is seeking to hold the companies accountable.

META CEO TO TESTIFY IN HIGH-STAKES TRIAL THAT COULD COST BIG TECH BILLIONS

Mark Zuckerberg, chief executive officer of Meta, arrives at a court in Los Angeles to testify in a landmark trial over social media addiction. (Kyle Grillot/Bloomberg via Getty Images)

Meta’s Instagram and Google’s YouTube deny the allegations, citing years of expanded safety features and parental controls as part of their defense. The tech titan is expected to point to other factors in K.G.M.’s life, highlight their investments in youth safety and argue they should not be held responsible for harmful content uploaded by users.

A verdict for the plaintiff could set a precedent for holding tech companies responsible for harmful design decisions, despite years of successfully invoking Section 230’s content liability shield — a federal law that largely shields online platforms from lawsuits related to user-posted content. A rejection of that defense could pave the way for similar lawsuits nationwide, exposing Meta and other tech companies to billions in potential damages and pressuring them to redesign their platforms.

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This is a developing story; check back later for updates.