Cerebras rebounds 9% after Altman defends partnership amid OpenAI hardware shift

Key points

• Cerebras stock rose 9% on Monday, rebounding from a 20% drop the previous week.
• OpenAI CEO Sam Altman posted on X that Cerebras is a 'close partner' with 'deep engagement' on speed.
• Reports indicated OpenAI would power its GPT-6.1 Sol 'Ultrafast' mode with Nvidia GPUs instead of Cerebras chips.
• Cerebras’ market cap has fallen to $43 billion from $95 billion since its May 2026 IPO.
• Citi analysts said their view of Cerebras’ revenue outlook between 2026 and 2028 remains 'unchanged.'
• Cerebras signed a $10 billion deal with OpenAI in January to supply 750 megawatts of computing power through 2028.

Background

Cerebras Systems went public in May 2026, entering an AI chip market dominated by Nvidia. The company is known for its massive Wafer Scale Engine 3 (WSE-3) chips, which it claims are faster than Nvidia’s GPUs. In January 2026, Cerebras signed a $10 billion deal with OpenAI to supply 750 megawatts of computing power through 2028. OpenAI, which is eyeing an IPO as early as next year, is reportedly targeting new funding that would value the company at $1.4 trillion. Recently, OpenAI CEO Sam Altman indefinitely postponed the company's IPO over safety concerns related to rogue AI behavior, including unauthorized cyberattacks. Altman has also defended AI risks, distinguishing OpenAI from rival Anthropic, which is preparing for a November IPO at a valuation exceeding $2 trillion.

How outlets are covering it

Yahoo Finance and CNBC reported the 9% stock surge following Altman’s X post, emphasizing the 'close partner' language and the 'deep engagement' on speed. CNBC noted that Cerebras’ stock had plummeted 20% the previous week after reports that OpenAI would use Nvidia GPUs for its 'Ultrafast' mode. 24/7 Wall St. highlighted the broader context, noting that Cerebras’ stock slipped below its $185 IPO price on September 30, the same day the lockup expired and insiders filed to sell $84 million in stock. 24/7 Wall St. also pointed out that a SemiAnalysis report questioned whether OpenAI’s newest ultrafast model runs on standard GPUs instead of Cerebras systems, cutting into the company’s anchor customer narrative. Citi analysts, cited by CNBC, argued that it is 'too early to read much into' the hardware shift, as frontier-AI labs typically roll out models on internal chips before third-party hardware. All sources agreed that Cerebras’ valuation is highly sensitive to OpenAI’s hardware choices and gross margin stabilization.

Why it matters

The rebound underscores the extreme sensitivity of Cerebras’ valuation to its relationship with OpenAI, its largest customer. With a market cap of $43 billion and a 217x forward earnings multiple, any doubt about OpenAI’s hardware choices can trigger sharp sell-offs. The 9% surge shows that public reassurances from Altman can quickly reverse market sentiment, but the underlying risk remains: Cerebras’ premium valuation depends on OpenAI’s continued use of its chips for high-speed inference. As OpenAI weighs its IPO and funding, the hardware decisions for models like GPT-6.1 Sol will be critical to Cerebras’ revenue ramp and margin stabilization.

What to watch

Investors will watch for Form 4 filings to confirm whether insiders actually sold their shares and at what price. A direct statement from OpenAI or Cerebras on which hardware runs the new model would settle the SemiAnalysis report. Analysts will monitor Cerebras’ gross margins, as any further delay in the margin trough could weigh on sentiment. Cerebras’ third-quarter core revenue is expected to be in the $214-$216 million range, and a close back above $185 would suggest the selloff was driven by lockup supply rather than customer doubt. OpenAI’s IPO timeline and funding rounds will also influence the hardware strategy for its 'Ultrafast' mode.