TLDR
- Cerebras stock dropped 7-9% after a report claimed OpenAI is using Nvidia chips instead of Cerebras hardware for its new “Ultrafast” AI tier.
- SemiAnalysis said OpenAI’s GPT-6.1 Sol Ultrafast mode runs on Nvidia GPUs at low batch size, not on Cerebras’ Wafer-Scale Engine.
- OpenAI is Cerebras’ largest customer by revenue backlog, and the two firms had publicly announced Cerebras would power Ultrafast mode in August.
- Neither Cerebras nor OpenAI has confirmed or denied the claim.
- The stock has struggled since its IPO in May, when it opened at $350.
Cerebras Systems stock fell sharply this week after a report questioned whether the company still has a role in powering OpenAI’s fastest AI model. The drop pushed the stock down as much as 8.87% during Wednesday’s session.
The trigger came from semiconductor research firm SemiAnalysis. It posted on social media that OpenAI’s new GPT-6.1 Sol Ultrafast model is running on standard Nvidia GPUs, not Cerebras’ specialized chips.
That claim matters a lot. OpenAI launched its “Ultrafast” tier promising speeds up to eight times faster than normal, around 300 tokens per second. Cerebras had been named as the partner behind that speed boost.
Cerebras built its entire pitch around solving exactly this kind of problem. Its Wafer-Scale Engine is a massive chip that fits billions of cores and huge memory pools onto one piece of silicon. That design avoids the slowdowns that come from shuffling data between hundreds of separate GPUs.
What the SemiAnalysis Report Actually Said
The key detail is a phrase buried in the report: “low batch size.” In AI inference, batching means grouping requests together so a GPU runs more efficiently.
Nvidia chips usually need large batches to hit peak performance. A low batch size means fewer requests processed at once, which favors speed over raw efficiency. That is the exact niche Cerebras has marketed itself around.
If OpenAI figured out how to run a top-tier model on Nvidia hardware at low batch size without losing cost efficiency, it chips away at one of Cerebras’ main selling points. That is why traders reacted fast.
Cerebras stock closed around $180.22 on Wednesday after the news spread. That is a steep fall from its IPO price of $350 back in May.
The IPO came with a lot of hype. Investors were excited about a chip company that claimed it could outperform Nvidia on raw inference speed for certain workloads.
That excitement has cooled since then. Earnings reports after the IPO failed to match the enthusiasm investors showed on day one.
Why OpenAI’s Involvement Matters So Much
OpenAI is not just another client for Cerebras. It is the company’s largest customer by revenue backlog, according to Barron’s.
Losing ground with OpenAI, even temporarily, raises real questions for investors. Cerebras has leaned heavily on its relationship with OpenAI to justify its valuation.
Neither Cerebras nor OpenAI has responded publicly to the SemiAnalysis report. That silence has left analysts guessing rather than confirming anything official.
There is also a chance this isn’t permanent. Capacity constraints or technical optimization issues could explain why Nvidia chips are handling the workload right now.
Cerebras could still end up powering Ultrafast mode down the road once any technical kinks get worked out. Nothing from either company rules that out yet.
For now, the stock reaction reflects uncertainty more than confirmed bad news. Investors are pricing in the risk that Nvidia’s CUDA ecosystem and hardware improvements make it tough for any challenger to lock in exclusive deals with major AI labs.
Cerebras has not issued any statement confirming or denying its current role in OpenAI’s infrastructure plans. As of Wednesday afternoon, the stock remained down close to 8% on the day.
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