Shares of Tempus AI plunged 7.1% to $65.68 on August 28, snapping a torrid rally that had lifted the stock more than 38% since August 18. The trigger: back-to-back selling disclosures from the company's most prominent institutional backer and its own chief executive, arriving just as the broader software sector posted gains—leaving no macro excuse for the selloff.
• ARK Dumped Nearly $8 Million in a Week, Signaling the Rally Outran Conviction. ARK sold 59,276 shares of Tempus AI through its ARKK ETF on August 27, worth roughly $4.1 million.
That followed a separate sale of 57,819 shares on August 25, valued at nearly $4 million.
Cathie Wood often trims her biggest winners after sharp rallies , but the cumulative size—about $8 million in three sessions—tells the market that even a true believer sees the stock as overextended. ARKK has seen roughly $1.7 billion in net outflows over the past 12 months , which means fund redemptions may also be forcing Wood's hand, amplifying supply pressure.
• The CEO's $16.3 Million in Sales Add an Uncomfortable Optics Problem. CEO Eric Lefkofsky trimmed an indirect position by 250,000 shares in late July through a pre-scheduled trading plan adopted in March.
He then sold another 132,591 shares on August 18 at $49.61 per share for about $6.6 million —one day before the stock surged 24%. Those sales were mandated to cover tax-withholding obligations and "do not represent a discretionary sale." Routine or not, roughly $16.3 million in combined insider dispositions in a month gives short-sellers ammunition.
• The Bull Case—A Cancer-Vaccine Windfall—Is Real but Priced Aggressively. The rally was sparked when Merck and Moderna reported a successful Phase 3 cancer vaccine trial that validated the genomic-sequencing technology behind Tempus's pending $1.5 billion acquisition of Personalis.
Tempus also posted its first-ever quarterly profit of $5.6 million, with revenue up 22% to $382.5 million.
Management raised 2026 revenue guidance to roughly $1.6 billion. Yet at a $12.7 billion market cap and negative trailing earnings, the stock trades at about 8× forward sales—a price that demands flawless execution on a deal that won't close until late 2026 at the earliest.
• Short Interest Could Cut Both Ways. More than 26% of outstanding shares are held short , a level that fueled the rally's ferocity but now provides a cushion of potential buyers if the selloff deepens. The next few sessions will reveal whether this is a healthy pullback or the start of a real unwind.