A federal judge overseeing a bellwether trial brought by 29 state attorneys general has barred Meta's economic expert from offering testimony about whether platform design features cause mental health harm. According to MLex, U.S.
District Judge Yvonne Gonzalez Rogers prevented economist Justin McCrary from testifying on causation or interpreting third-party research outside his expertise, while Law360 reports she approved the states' damages expert to testify about Meta's profits from teen users and engagement metrics. The August 2026 trial signals how courts now treat expert testimony in platform liability cases, where the contested issue is no longer whether social media causes addiction, but whether algorithmic features constitute defective product design subject to liability. This asymmetry—blocking the defendant's causation expert while permitting the plaintiff's damages expert—changes the evidentiary landscape in dozens of pending social media addiction cases nationwide.
Table of Contents
- What Expert Testimony Meta Lost
- What Expert Testimony the States Keep
- Design Liability Bypasses Section 230
- Precedent From the March 2026 Verdict
- If You Used These Platforms as a Teen or Parent
- What Comes Next in This Trial
What Expert Testimony Meta Lost
According to MLex, Meta sought economist Justin McCrary as a rebuttal expert but Judge Gonzalez Rogers barred him from testifying about whether design features cause addiction or mental health harms and from interpreting third-party research outside his expertise. This restriction removes Meta's primary tool for attacking the causal link between platform mechanics and teen harm that the states planned to establish through their own expert witnesses.
Causation is typically the pivotal issue in product liability cases. By preventing Meta's expert from offering competing causation testimony, the judge constrained Meta's ability to present a complete defense. McCrary might testify about platform profits or economic damages, but not about the biological or psychological mechanisms connecting design to harm—forcing Meta to rely on cross-examination rather than expert rebuttal.
What Expert Testimony the States Keep
According to Law360, Judge Gonzalez Rogers denied Meta's motion to exclude Carl Saba, the states' damages expert, allowing him to testify on Meta's profits from teen users, time-spend metrics on facebook and Instagram, harmful algorithmic encounters, and estimated under-13 usage. This approval means the jury will hear evidence directly linking specific design choices—algorithmic recommendations and engagement metrics—to measurable business outcomes.
Saba's testimony creates a pathway for jurors to infer that Meta knowingly prioritized engagement over teen safety, a key element in both negligence and strict product liability theories. Unlike defense expert testimony on causation, which courts sometimes exclude as speculative, damage estimates and profit data are typically admissible because they rest on financial records and platform analytics rather than opinion on scientific causation.
Design Liability Bypasses Section 230
According to Courthouse news Service, Judge Gonzalez Rogers permitted design-defect, negligence, and failure-to-warn claims targeting algorithmic recommendations and engagement mechanisms to proceed despite Meta's Section 230 arguments. The distinction is critical: Section 230 shields platforms from liability for user-generated content, but not for how the platform itself is engineered.
This doctrinal shift explains why expert testimony on design defects is now central to social media liability cases. If the alleged defect is the algorithm—not the content it recommends—then product liability standards apply, and expert testimony about causation, foreseeability, and alternative designs becomes admissible and potentially dispositive. Courts are now willing to treat engagement-optimization algorithms the same way they treat defective car brakes or pharmaceutical dosing mechanisms.
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Precedent From the March 2026 Verdict
According to Al Jazeera, the March 2026 K.G.M. v. Meta verdict found Meta 70% liable and YouTube 30% liable, awarding $6 million in damages—the first major product liability verdict against social media platforms.
Hollingsworth LLP reports that psychiatric and neuroscience expert testimony linking Facebook and Instagram's features to teen addiction was accepted by jurors in that trial. The August 2026 federal trial differs in structure: it will use an advisory jury on addictiveness claims while Judge Gonzalez Rogers decides Children's Online Privacy Protection Act violations herself. However, the expert testimony restrictions hit harder here because Meta has lost its primary causation rebuttal layer. If the jury returns a substantial verdict despite these constraints on Meta's defense, the precedent will accelerate settlement negotiations in other pending cases.
If You Used These Platforms as a Teen or Parent
If you are a minor or parent of a minor who used Facebook or Instagram, these expert testimony rulings strengthen your legal position in pending lawsuits. The restriction on Meta's causation expert removes a key defense, and approval of damages testimony means courts are willing to hear evidence linking your teen's time on platform, algorithmic exposure to harmful content, and mental health consequences to Meta's business model.
Pending cases against Meta and YouTube typically allege that engagement-optimizing algorithms, features designed to maximize time-spend, and internal knowledge of mental health risks constitute design defects. According to Bloomberg Law, courts now treat algorithmic recommendation systems, engagement metrics, and addiction-optimization features as defective product designs subject to tort remedies—opening a damages pathway that did not exist five years ago.
What Comes Next in This Trial
The August 2026 bellwether trial is reaching its expert testimony phase. Expert evidence will shape how jurors weigh platform addiction science against Meta's economic incentives and internal knowledge of teen mental health risks.
The verdict will likely influence settlement posture in dozens of pending state and federal cases and may signal to other platforms what expert testimony courts will accept on platform design liability. If the jury returns a substantial damages award or finds platform design defective despite Meta's limited rebuttal evidence, defendants will face pressure to settle rather than litigate to trial. The restricted expert testimony available to Meta in this case creates an unusually favorable evidentiary posture for plaintiffs—a dynamic that is likely to accelerate both settlements and class certification decisions in similar cases across the country.
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