Senators put TikTok's 15 million-user control group on a Sept. 1 clock

Republican Marsha Blackburn of Tennessee and Democrat Richard Blumenthal of Connecticut sent a four-page letter on Wednesday to TikTok Inc. chief executive Shou Chew and to Adam Presser, chief executive of the company's US spinoff, demanding answers about an experiment that withheld a safety feature from millions of American users, one of them a teenager who died by suicide ^[1][2]. They set a Sept. 1 deadline for a response ^[16], which is the point at which a magazine investigation stops being a reputational event and becomes a dated paper trail.

The underlying record is a confidential 2023 TikTok document, reported this month by Bloomberg Businessweek, that was handed over in litigation against the world's biggest social media companies and placed under a court-ordered seal ^[5][6]. According to the document, TikTok intentionally switched off an algorithmic safeguard designed to break up online echo chambers of harmful content for 10% of US users, turning them into a control group that would have numbered approximately 15 million people ^[7][8]. Taken at face value, that ratio implies a US user base of roughly 150 million at the time ^[9].

The sentence that will get read aloud is the document's own accounting: the choice was "a delicate balance across safety and the ability to measure impact on DAU (daily active users) and core metrics" ^[12]. Chase Nasca, a 16-year-old from Bayport, New York, was randomly selected into the experiment on Jan. 25, 2022, was fed thousands of videos about sadness, hopelessness, loneliness and suicide, and was dead within a month ^[10]. The document's explanation for the content he saw: "TikTok's filter bubble prevention strategies did not take effect on this user by design" ^[11].

The two senators are co-sponsors of an online child safety bill and called the decision to run the test "depraved" ^[4]. Their letter argues the revelations are "made even more sinister" because Congress had raised concerns about TikTok's algorithm driving young users toward harmful content since October 2021, before the experiment was rolled out ^[13]. That framing does two jobs at once: it supplies a notice argument useful to plaintiffs, and it supplies a legislative predicate.

The asks are shaped like discovery. Thirteen questions, including the name of every employee informed of the experiment, an explanation for why minors were included, when executives learned of it, and a complete, unredacted version of the sealed document ^[14]. Then the expensive one: a list of every algorithmic experiment in the US in which TikTok withheld, disabled, delayed or reduced a safety feature, with the number of users involved and how many were minors ^[15]. If that list is long, the story is no longer one experiment.

TikTok did not respond to Fortune's request for comment on the letter; a spokesperson told Businessweek the company is "deeply committed to the safety and well-being of users," especially teens, and continues to invest significantly in Trust and Safety ^[17]. Blackburn, in an interview after the Businessweek story and before the letter, said the conduct "just seems inconceivable" and framed it as a company prioritising "making money and capturing eyeballs" ^[18][19].

Watch three things by Sept. 1: whether TikTok produces the unredacted document to Congress or hides behind the seal, whether it concedes that a portfolio of safety-withholding experiments exists, and whether Presser answers separately from Chew. Naming the spinoff's chief executive on the same letterhead as the parent's is the part that transfers liability to the new US entity.