Cerebras Systems shares fell sharply this week after semiconductor research firm SemiAnalysis reported that OpenAI’s newest flagship model is not running on Cerebras hardware. The stock dropped as much as 8.87% during Wednesday’s session and closed around $180.22, down from its IPO price of $350 in May.
The report claimed that OpenAI’s GPT-6.1 Sol Ultrafast model is being served on Nvidia GPUs at low batch size, rather than on Cerebras’ Wafer-Scale Engine chips. That detail matters because Cerebras has built its pitch around high-speed inference at low batch sizes, a niche where it claimed advantages over Nvidia hardware.
OpenAI is Cerebras’ largest customer by revenue backlog, so any sign that the relationship is weakening carries outsized weight for investors. In August, Cerebras had announced it would power the Ultrafast tier for GPT-5.6 Sol at speeds up to 750 tokens per second. The new GPT-6.1 Sol Ultrafast tier, unveiled at OpenAI’s DevDay on September 29, reportedly runs at only around 300 tokens per second.
Neither Cerebras nor OpenAI has confirmed or denied the report. The lack of official comment has left analysts uncertain whether Nvidia’s role is temporary due to capacity or optimization issues, or a longer-term shift. Cerebras could still power later versions of Ultrafast mode if technical issues are resolved.
The stock was already under pressure before the news. Cerebras posted a GAAP net loss of $450.5 million in its most recent quarter, and insiders sold roughly $266 million in stock over the past three months. Shares are now trading closer to their 52-week low of $160.81 than their 52-week high of $386.34. Meanwhile, Nvidia rose about 2% on Wednesday, while the Nasdaq climbed 0.9%.
