TikTok's A/B safety test left 15 million U.S. users without protection, preceding a teen suicide

Internal documents obtained by Bloomberg show that TikTok ran an A/B safety experiment in early 2022, keeping the older recommendation algorithm for roughly 10 percent of its U.S. user base – about 15 million people. The test was meant to gauge whether a newer safety‑focused feed would reduce user "stickiness" and improve engagement metrics.

One member of the control group was 16‑year‑old Chase Nasca of Long Island, New York. Because his account remained on the older algorithm, his feed was filled with videos about suicide, self‑harm and depression. Nasca died by suicide in February 2022. TikTok later said the experiment was routine, that it has refined its testing practices, and that future tests should involve a control group of under 1 percent and a much shorter duration.

The document surfaced amid broader litigation over platform safety, and TikTok issued a statement expressing condolences and reaffirming its commitment to user well‑being.