What happened this week
A Wednesday post from research outfit SemiAnalysis on X said OpenAI will tap Nvidia graphics chips, not Cerebras hardware, for the "Ultrafast" setting tied to GPT-6.1 Sol. The timing lined up with a rough week for Cerebras shares, which tumbled close to 20% and hit their lowest level since the company's big May debut. Friday's close landed at $166.43, before a late pop in extended trading.
The locking, the selling, and the math
Fresh supply also weighed on the tape. According to the company's prospectus, beginning Wednesday up to 19.4 million shares owned by directors, officers, nonexecutive employees, and other nonemployee holders were unlocked for trading, which works out to 8% of the company's shares outstanding. Before that date, as many as 14.6 million shares had been released on a biweekly schedule starting Aug. 19.
Insider sales have been sizable. Acting under trading programs set up soon after the IPO, CEO Andrew Feldman and CTO Sean Lie sold more than $240 million in Class A stock from Aug. 20 through Sept. 25, and other executives also sold holdings valued in the millions. Cerebras finished its first day as a public company at a $95 billion valuation; today that figure is just over $39 billion.
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The product relationship at the center
Cerebras makes dinner plate-sized ASICs tailored for inference and offers them as a cloud service from its own data centers. In January, it agreed to supply OpenAI with 750 megawatts of compute through 2028 in a deal valued at over $10 billion. Handoffs of inference work matter here: McKinsey expects inference to overtake training as the dominant AI data center task by the end of the decade, so the idea of OpenAI running Ultrafast on Nvidia takes some air out of the "alternative to Nvidia" trade.
What this means for your portfolio
This was a cocktail of headline risk and share unlocks. After the chatter, OpenAI's Sam Altman posted, "Cerebras is a close partner, and we have a deep engagement pushing on the frontiers of speed," and the stock bounced in the after-hours session to 171.51, up 5.08 (+3.05%), from a regular close of 166.43, down 3.09 (-1.82%). With investors hunting for alternatives to Nvidia, who handles OpenAI's inference load matters, and so does an unlock calendar that keeps adding supply. Watching concrete customer allocations and those unlock dates helps explain moves like this.
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