Instagram head Adam Mosseri is set to testify on Wednesday in a landmark trial involving claims that social media platforms owned by Meta and the video sharing platform YouTube are designed to be addictive for younger users.

The social media boss of Instagram, a subsidiary of Meta, will take the stand Wednesday, Feb. 11, to give testimony in the trial, which marks the first time major tech giants will face a jury over these allegations.

According to Meta, Mosseri “oversees all functions” of the Instagram app, “including engineering, product and operations.” He has worked for Meta for over a decade, previously serving as design director for mobile apps before leading the News Feed product and engineering teams, according to his company bio.

The social media case is being heard in the California Superior Court of Los Angeles County, with Meta, Facebook and Instagram’s parent company, and YouTube, which is owned by Google, moving forward as defendants.

Social platforms Snapchat and TikTok were previously named in the lawsuit but reached settlements with the plaintiffs last month.

Opening statements began earlier this week, with lawyers for both Meta and YouTube addressing the court on Monday and Tuesday, respectively.

This case centers around a 20-year-old plaintiff who goes by the initials KGM, whose lawyers claim she became hooked on social media apps starting at age 6. She says features like autoscrolling got her addicted to the platforms, ultimately leading to anxiety, depression and body image issues.

“Borrowing heavily from the behavioral and neurobiological techniques used by slot machines and exploited by the cigarette industry, defendants deliberately embedded in their products an array of design features aimed at maximizing youth engagement to drive advertising revenue,” the lawsuit claims, pointing to features on social media apps like auto-scrolling.

The social media companies deny the allegations. They have argued that other factors contribute to the mental health of young social media users and that they have put in place guardrails to protect them, including specific parental controls for accounts belonging to children and teens.

In a previous statement to ABC News, a Meta spokesperson said, “We strongly disagree with these allegations and are confident the evidence will show our longstanding commitment to supporting young people.”

Meta said that the company has made “meaningful changes” to its services, such as introducing accounts specifically for teenage users.

In a separate statement to ABC News on Wednesday, a Meta spokesperson added, “The question for the jury in Los Angeles is whether Instagram was a substantial factor in the plaintiff’s mental health struggles. The evidence will show she faced many significant, difficult challenges well before she ever used social media.”

 YouTube has also said the allegations in the lawsuit are “not true.”

“Providing young people with a safer, healthier experience has always been core to our work,” spokesperson José Castañeda said in a statement to ABC News previously. “In collaboration with youth, mental health and parenting experts, we built services and policies to provide young people with age-appropriate experiences, and parents with robust controls.”

Meta CEO Mark Zuckerberg is expected to take the witness stand during the trial, with testimony currently set for Feb. 18.

Editor’s note: This article has been updated to include new comments from a Meta spokesperson.