OpenAI CEO Sam Altman Called Cerebras a ‘Close Partner.’ Its Stock Surged.

Cerebras Systems shares jumped on Monday after OpenAI CEO Sam Altman moved to calm concerns about the artificial intelligence chipmaker's relationship with one of its most important partners.

The stock rose as much as 9.5% during Monday trading, rebounding from a sharp selloff last week after investors learned that OpenAI was using Nvidia graphics processing units, rather than Cerebras chips, to power the new "Ultrafast" mode for GPT-6.1 Sol.

Altman addressed the speculation directly Friday in a post on X. "There is some speculation about our partnership with Cerebras," Altman wrote.

"Cerebras is a close partner, and we have a deep engagement pushing on the frontiers of speed." The comments provided immediate relief for Cerebras investors.

The rebound comes after a bruising week for Cerebras, which lost roughly 20% and touched its lowest level since its blockbuster Nasdaq debut in May. The company's market capitalization has fallen dramatically from the levels reached around its public debut, reflecting growing investor scrutiny over its valuation, margins and ability to compete with Nvidia in the rapidly expanding AI infrastructure market.

At the center of last week's selloff was OpenAI's decision to rely on Nvidia hardware for GPT-6.1 Sol's Ultrafast offering. The move raised questions about whether Cerebras was losing ground at a particularly important customer. Altman's statement suggested investors may have read too much into the decision.

OpenAI and Cerebras announced a major multi-year partnership in January under which Cerebras will provide 750 megawatts of ultra-low-latency AI computing capacity. The capacity is scheduled to come online in stages through 2028. OpenAI said at the time that Cerebras would become part of a broader computing portfolio designed to match different hardware systems with different AI workloads.

Rather than relying on conventional GPUs, the company builds enormous wafer-scale processors designed specifically for AI workloads. Its technology combines computing power, memory and bandwidth on a single chip in an effort to eliminate bottlenecks and generate AI responses at much higher speeds.

OpenAI has previously said integrating Cerebras into its infrastructure could produce faster responses, more natural interactions and better performance for demanding applications such as coding and AI agents.

Wall Street analysts also cautioned against interpreting OpenAI's use of Nvidia for one product as evidence of a broader deterioration in the Cerebras relationship. In a note seen by CNBC, Citi analysts said their expectations for Cerebras revenue between 2026 and 2028 remain "unchanged," arguing that "We believe frontier-AI labs' latest models would initially roll out on internal chips before running on third-party or Cerebras cloud, so it's too early to read much into it."

Citi also said "the stock's ability to outperform is increasingly tied to evidence that gross margins are stabilizing. Any further delay in the gross margin trough would likely weigh on sentiment, particularly given Cerebras' premium valuation."