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Cerebras shares fell roughly 20% over the reported week as investors weighed an unconfirmed report that OpenAI was serving one model on Nvidia GPUs, alongside the September 30 expiry of Cerebras’ IPO lockup. The reported model-level use is not evidence that OpenAI ended or changed its broader Cerebras agreement; the lockup made shares eligible for resale but does not establish that insiders sold.
What triggered the decline?
Two developments drew attention: a report about which hardware OpenAI may use for a particular model, and a scheduled lockup expiry that made some Cerebras shares eligible for sale. The weekly decline is reported as roughly 20%; the available reporting does not provide a price series to establish an exact closing-to-closing calculation.
The Nvidia report concerned one model
Investing.com reported that Cerebras fell 6.3% in morning trading after SemiAnalysis posted that OpenAI’s GPT-6.1 Sol Ultrafast was being served on Nvidia GPUs, potentially Blackwell-class GPUs. Investing.com described the claim as needing clarification. This is secondhand reporting: the materials available do not include OpenAI or Cerebras confirmation of that specific arrangement. Investing.com report
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsA model being served on a different supplier’s hardware would raise questions about product allocation, but it would not by itself show that OpenAI had abandoned Cerebras or changed the broader agreement. The reported claim is narrower than a change to the overall customer relationship.
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The lockup expiry added potential supply
24/7 Wall St. reported that Cerebras’ September 30 post-IPO lockup expiry made about 19.4 million shares eligible for sale. That figure describes potential resale eligibility, not completed sales. The outlet also reported Form 144 notices covering about $84.3 million in intended sales by officers; a Form 144 is a notice of a proposed sale, not proof that a transaction occurred. 24/7 Wall St. report
Eligibility for resale can affect investor expectations about available supply, but it should not be treated as evidence that insiders actually sold or as proof that lockup-related selling caused the decline.
What does the OpenAI-Cerebras agreement establish?
Cerebras said in 2026 that its multi-year OpenAI agreement was valued at more than $20 billion and covered 750 megawatts of inference capacity over several years. These are company-reported contract value and capacity commitments; they do not mean all of that capacity had already been deployed. Cerebras’ June 23, 2026 results release
The agreement’s scale is relevant context, but it does not verify how OpenAI allocates a particular model across suppliers. Nor does use of Nvidia for one reported model establish that the multi-year agreement has been terminated or reduced. Cerebras CEO Andrew Feldman said in the same release: “AI has moved from being a novelty to being useful and productive.”
What do Cerebras’ customer disclosures show?
Cerebras’ first-quarter 2026 Form 10-Q reported that Customer A represented 63% of quarterly revenue and Customer B represented 11%. The table identifies customers by letter, so those figures should not be attributed to OpenAI based on the table alone. They are a snapshot of one quarter’s revenue mix, not a measure of the value or deployment status of the entire multi-year OpenAI agreement. Cerebras Systems Form 10-Q, 2026
The concentration figures highlight that a small number of customers accounted for a large share of that quarter’s revenue. They do not establish that a customer relationship ended, and they cannot resolve the specific GPT-6.1 Sol hardware report.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How does Nvidia fit into OpenAI’s broader infrastructure?
Axios reported that OpenAI was testing a homegrown chip, used Nvidia for training, and had recently begun using Cerebras for inference. That account illustrates a multi-supplier environment in which different workloads may use different systems. It does not confirm the separate claim about GPT-6.1 Sol Ultrafast. Axios report
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What investors can—and cannot—infer
- Reported model allocation: A secondhand claim about one model’s serving hardware may affect expectations, but it is not company confirmation of a broader contract change.
- Lockup expiry: The September 30 event made shares eligible for resale. Reported Form 144 notices describe intended sales; they do not confirm completed transactions.
- Customer concentration: The Form 10-Q figures describe first-quarter revenue concentration by anonymized customer labels, not the identity of either customer or the full economics of a multi-year agreement.
These are concurrent considerations, not proof of a single cause for the share move. The available facts support investor concern about allocation uncertainty and possible share supply; they do not establish that OpenAI ended its Cerebras deal or that notified sales were executed.
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