Cerebras Systems Inc (NASDAQ:CBRS) shares are falling Wednesday after short seller Culper Research published a report claiming the chipmaker’s wafer-sized processors wear out too quickly. Here’s what you should know.
- Cerebras Systems stock is showing notable weakness. What’s weighing on CBRS shares?
Cerebras Stock Falls After Culper Short Report
Short seller Culper Research, which says it’s betting against Cerebras, released a report Wednesday claiming the company’s giant chips break down after 18 to 30 months in service. Culper argues that a lifespan that short calls the company’s business model into question.
Cerebras did not immediately respond to Benzinga’s request for comment.
Culper disclosed that it’s short Cerebras and expects shares to fall from current levels. Its disclaimer tells readers to assume the firm may trade immediately after publication and could flip between long and short at any time. It’s worth noting that some of the short seller’s evidence comes from unnamed ex-staff and customers, and the firm considers its conclusions opinions.
Culper Questions Cerebras’ Chip Design
Thermal expansion is the central issue. When heated, a giant chip and the board under it expand unequally, and repeated cycles can wear out the links that join them. Andrew Feldman, Cerebras’ chief executive, credits the fix to a special connector material that the company “had to invent.” Culper disagrees. The firm says the material is PariPoser, developed at Bell Labs in the 1980s and now sold by Paricon Technologies, a small Massachusetts company.
Culper alleges that Cerebras sidesteps the problem by running filler computations, which the firm calls dummy operations, so its wafers never cool. Its evidence includes comments a Cerebras solutions architect made in Berlin in June 2026 and code it decompiled from Cerebras’ client software.
Culper also points to an April 2026 Harvard and Meta study that measured the CS-3 pulling 80% of its rated power at rest, versus 20% for GPUs made by Nvidia and AMD. In Culper’s model, that constant draw makes wafers age 3 to 3.5 times as fast as GPUs.
Culper Flags Cerebras’ Accounting, OpenAI Deal
On accounting, Culper flagged a change in a key assumption. Draft filings through December 2025 assumed Cerebras’ computers last 1.5 to 3 years, and the April 2026 S-1 stretched that to 3 to 5 years, a change Culper says came with no explanation. Culper recalculated: at 2.25 years, first-half gross margin drops to 24.0% from the 29.9% Cerebras reported.
Culper also challenges the December 2025 OpenAI agreement. By its math, OpenAI pays 20% to 77% less than hardware buyers. If wafers hold up only 2.5 years, Culper says the contract could range from about even for Cerebras to a negative net present value of $13.8 billion.
Culper points to share supply as well. It says 19.4 million shares became eligible for sale Wednesday and more than 50 million others become tradable in early November. Insiders have cashed out over $400 million of shares since the company went public, Culper says, and early private investors bought in around $23 a share, roughly a fifth of the current price.
CBRS Shares Are Slipping
CBRS Price Action: Cerebras shares were down 5.20% at $113.11 at the time of publication on Wednesday. The stock is trading near its 52-week low of $106.13, according to Benzinga Pro.
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