Cerebras Falls About 7% on SemiAnalysis Report That OpenAI's Newest Ultrafast Tier Runs on Nvidia GPUs

CBRS shares gapped down on Wednesday, September 30, opening at $183.69 against a prior close of $194.95, a 6.7% drop, and later traded at $177.65 on volume well above average. The trigger was a SemiAnalysis report that it believes OpenAI's newly launched GPT-6.1 Sol Ultrafast mode is running at low batch sizes on NVDA GPUs rather than on Cerebras' wafer-scale systems. The claim is an inference rather than a confirmed fact: Cerebras had not commented, and OpenAI has not said what hardware serves the tier.

The report landed on Cerebras' most sensitive point. In August, Cerebras said it powered the earlier GPT-5.6 Sol Ultrafast mode at up to 750 output tokens per second, and OpenAI accounted for $56.8 million of Cerebras' $180.1 million in second-quarter revenue, about 32%, according to the company's 10-Q. Barron's framed the slide as a reflection of how much Cerebras depends on OpenAI, and the shares slipped below the $185 IPO price during the selloff.

Insider filings added to the noise but were not a reaction to the report. Form 4s show chief operating officer Dhiraj Mallick sold 396,000 shares on September 29 at an average of $204.04, about $80.8 million, and chief accounting officer Yagnesh Patel sold 1,320 shares on September 28 for $269,940, both under Rule 10b5-1 trading plans; the COO's plan was adopted June 30. Options traders bought 45,379 calls, about 14% above average volume.

What to watch: whether OpenAI or Cerebras clarifies the hardware behind the GPT-6.1 tier, and progress on Cerebras' $25.4 billion backlog, much of it tied to its multi-year OpenAI agreement. Cerebras last reported on August 12, posting GAAP revenue up 74% and raising full-year core revenue guidance to $880 million to $890 million.