Key TakeawaysShares of Cerebras Systems declined approximately 7% on September 30 following a SemiAnalysis industry report.According to the report, OpenAI’s recently launched GPT-6.1 Sol Ultrafast model operates on Nvidia hardware rather than Cerebras chips.OpenAI represents Cerebras’ most significant customer measured by revenue backlog.The new Ultrafast tier allegedly delivers approximately 300 tokens per second, significantly lower than the 750 tokens achieved by the previous model.CBRS shares are currently trading much nearer to their 52-week low compared to their annual peak.Shares of Cerebras Systems experienced a roughly 7% decline to $181.40 during Wednesday trading. 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.Cerebras Systems Inc., CBRSAccording to the analysis, GPT-6.1 Sol Ultrafast is being deployed on Nvidia infrastructure instead. This hardware could potentially include Blackwell-generation chips like the GB300.Both Cerebras and OpenAI have yet to issue official statements regarding these claims. In the absence of direct confirmation, some ambiguity persists concerning the actual infrastructure configuration.The Significance of This DevelopmentOpenAI stands as Cerebras’ most important customer when measured by committed revenue backlog. Any potential loss of business with this single client carries disproportionate implications for the stock’s performance.The chronology of events adds another layer of concern. This past August, Cerebras publicly revealed it would supply the processing power for the Ultrafast tier of GPT-5.6 Sol, achieving performance speeds reaching 750 tokens per second.This announcement was positioned as a major victory for the company’s proprietary Wafer-Scale Engine chip architecture. However, the newly introduced GPT-6.1 Sol Ultrafast tier, which OpenAI revealed during its DevDay event on September 29, allegedly operates at merely around 300 tokens per second.This reduced performance metric has sparked speculation about whether the expanded model may be encountering constraints related to Cerebras’ on-chip memory architecture. Such technical specifications typically remain beneath investor attention, but this week proved different.Mounting Challenges for the StockWednesday’s share price decline represents just the latest setback. Cerebras has experienced a turbulent journey since its initial public offering debuted at $350 per share in May.The chipmaker reported a GAAP net loss totaling $450.5 million during its latest quarterly filing. Additionally, company insiders have 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 compared to the 52-week high of $386.34. This 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 opposing direction with approximately 2% gains.An alternative interpretation exists where the fundamental business relationship remains intact long term. 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.The post Cerebras Systems (CBRS) Stock Plunges 7% on OpenAI-Nvidia Partnership Reports appeared first on Blockonomi.