Cerebras Systems Inc. shares climbed 7.37% to $178.70 on Monday after OpenAI CEO Sam Altman publicly reaffirmed the company's role as a key inference partner, reversing part of a near 20% decline triggered by a report that OpenAI's latest model ran on Nvidia hardware.

Altman pushes back on partnership concerns

The rebound followed a post by Altman on X, where he stated: "Cerebras is a close partner, and we have a deep engagement pushing on the frontiers of speed." The comments came after a SemiAnalysis report said OpenAI's GPT-6.1 Sol Ultrafast speed tier was running on Nvidia Corp GPUs rather than Cerebras chips, raising investor concerns about the chipmaker's competitive position. Neither OpenAI nor Cerebras had publicly confirmed the hardware configuration for that tier.

OpenAI and Cerebras announced a multiyear agreement in January for 750 megawatts of Cerebras inference capacity through 2028. OpenAI said at the time that Cerebras would add a dedicated low-latency solution to its compute portfolio, with the goal of delivering faster responses across workloads.

Speed is becoming a market

The broader debate centres on inference, the computing required every time a user asks a question, generates code, or interacts with an AI agent. Cerebras has built its investment case around making that process faster. The company said its cloud business grew 281% year over year, while data-centre capacity live or under contract surpassed 600 megawatts. It also said manufacturing capacity was set to increase more than 10 times in 2026.

Mizuho analyst Vijay Rakesh estimates the fast-inference market could reach $550 billion by 2030, representing roughly 20% of AI workloads. He reiterated an Outperform rating and a $300 price target on Cerebras shares.

Nvidia still holds scale advantage

Nvidia's advantage lies in the breadth of its ecosystem and its ability to serve everything from model training to inference. Cerebras is taking a narrower approach, betting that workloads where milliseconds matter can justify specialised hardware. The OpenAI situation is therefore important for both stocks: if AI applications increasingly require real-time responses, inference could become a market large enough for multiple architectures.

Share unlock and market context

The Monday rebound follows a difficult prior session in which Cerebras shares fell 5.76% to $183.85, pressured by the release of approximately 19.4 million shares as part of the company's staggered IPO lockup expiration. That expiration releases shares in 11 separate waves, with two larger tranches remaining, scheduled for October 14 and October 28. Together, those three specific releases are set to free about 58 million additional shares for trading. The entire lockup period expires no later than November 9.

For investors, the question is no longer simply whether Cerebras can take share from Nvidia. The question is whether fast inference becomes a sufficiently large and valuable category for Cerebras to build a durable business within it. The next proof points are capacity deployment, new customers beyond OpenAI, and whether the company's speed advantage translates into improving margins.