Cerebras Systems Inc. (CBRS) shares fell by roughly 7% to $181.40 during Wednesday trading on September 30. The sell-off followed a report from semiconductor analysis firm SemiAnalysis indicating that OpenAI's latest flagship artificial intelligence model is not utilizing Cerebras chip technology, despite the company's prominent role in powering the previous version.

According to the analysis, the newly launched GPT-6.1 Sol Ultrafast model is being deployed on Nvidia infrastructure instead, with the hardware potentially including Blackwell-generation chips such as the GB300 — Blackwell being Nvidia's flagship data-center chip family. Neither Cerebras nor OpenAI has issued an official statement regarding the claims, and in the absence of direct confirmation, some ambiguity persists concerning the actual infrastructure configuration behind the high-speed tier.

Why the Customer Relationship Matters

OpenAI stands as Cerebras' most significant customer when measured by committed revenue backlog — contracted revenue the company has already secured but has yet to recognize — which means that any potential loss of business with this single client carries disproportionate implications for the stock's overall performance. By that measure, no other client matches OpenAI in importance to the chipmaker.

The chronology of events adds another layer of concern. In August, Cerebras publicly revealed that it would supply the processing power for the Ultrafast tier of GPT-5.6 Sol, achieving performance speeds reaching 750 tokens per second. That announcement was positioned as a major victory for the company's proprietary Wafer-Scale Engine chip architecture.

The newly introduced GPT-6.1 Sol Ultrafast tier, which OpenAI unveiled during its DevDay event on September 29, allegedly operates at only around 300 tokens per second — well below the 750 tokens achieved by the previous model. Tokens are the basic units of generated model output, so the metric maps directly onto how quickly users receive responses — and because Ultrafast tiers are pitched on speed, that figure doubles as the headline selling point for whichever chip powers the service. The reduced performance metric has fueled speculation about whether the expanded model may be running into constraints tied to Cerebras' on-chip memory architecture. Technical specifications like these typically remain beneath investor attention, but this week proved different.

Mounting Challenges for the Stock

Wednesday's share price decline represents only the latest setback for a company that has experienced a turbulent journey since its initial public offering debuted at $350 per share in May. In its latest quarterly filing, the chipmaker reported a GAAP net loss totaling $450.5 million. Company have additionally divested approximately $266 million worth of shares throughout the preceding three-month period.

Current share prices sit substantially closer to the 52-week low of $160.81 than to the 52-week high of $386.34. That substantial range illustrates how dramatically investor sentiment has deteriorated since the company went public.

The overall market conditions provided no assistance for Cerebras on Wednesday. The S&P 500 posted gains for the day, while the Nasdaq advanced 0.9%. This divergence positioned Cerebras among the most notable underperformers within the semiconductor sector during the trading session. Nvidia, by contrast, headed in the opposite direction with gains of approximately 2%.

An alternative interpretation holds that the fundamental business relationship remains intact over the long term, and that Cerebras could potentially power subsequent iterations of Ultrafast mode once capacity limitations or optimization challenges are resolved. At present, however, the market is responding to the immediate news rather than speculative future possibilities — and that immediate news presents unfavorable optics for Cerebras.

As of Wednesday morning trading, Cerebras stock was positioned around $181.40, representing a substantial retreat from its 52-week peak of $386.34. Neither company has released additional commentary regarding the reported infrastructure transition. Until one of them does, the clearest signals to watch are an official statement from either side or customer-related disclosures in Cerebras' future quarterly filings — the same channel through which its $450.5 million loss was reported.

Source: Blockonomi — Cerebras Systems (CBRS) Stock Plunges 7% on OpenAI-Nvidia Partnership Reports