Cerebras shares rebounded from a brutal week, climbing sharply on Monday after OpenAI CEO Sam Altman publicly reaffirmed the partnership between the two companies, lifting sentiment around the AI chipmaker.

In a Friday post on X, Altman directly addressed speculation about the relationship between the two firms, describing Cerebras as a "close partner" of OpenAI and saying the two are "deeply collaborating at the frontier of speed."

Buoyed by those comments, Cerebras shares jumped more than 10% at one point on Monday.

The rally followed a week in which Cerebras shares tumbled 20% in total, touching their lowest level since listing on the Nasdaq. The trigger was OpenAI's decision to use NVIDIA GPUs, rather than Cerebras chips, for the "Ultrafast" mode of GPT-6.1 Sol, sparking fears that its core customer relationship was wavering.

NVIDIA Chips Replacing Cerebras Spark Panic

The main cause of Cerebras' steep decline last week was the market's interpretation of OpenAI's hardware choices. According to CNBC, when OpenAI launched the "Ultrafast" mode of GPT-6.1 Sol, it chose NVIDIA (NVDA) graphics processors to power the feature, rather than Cerebras' specialized chips.

The news worried investors, who believed OpenAI was gradually shifting its core inference workloads toward NVIDIA, potentially sidelining Cerebras' strategic position.

Cerebras specializes in developing and producing AI computing systems, and its chips are known for their very large size and faster processing of AI workloads, positioning them as a competing alternative to traditional GPUs.

In January, Cerebras signed a $10 billion agreement with OpenAI to supply 750 megawatts of computing capacity over a contract term running through 2028.

Analysts: 2028 Revenue Forecasts Unchanged for Now, but Gross Margin Trend Is Key

Despite the sharp share price swings, some Wall Street analysts have adopted a cautiously optimistic stance.

Citi analysts said on Friday that their revenue forecasts for Cerebras through 2028 had not changed as a result of the news. "We believe the latest models from frontier AI labs will initially launch on internal chips before transitioning to third-party or Cerebras cloud operations, so it is too early to read too much into this now."

However, Citi also flagged a risk: until gross margins bottom out and stabilize, any further decline could weigh on investor confidence — especially given that Cerebras' current valuation remains at elevated levels.

Background: Pressure Since Listing, OpenAI Seeking Massive New Funding

Cerebras completed its listing in May of this year, entering the NVIDIA-dominated AI chip market with a high-profile valuation of nearly $95 billion.

Since listing, however, the company's shares have remained under pressure — in mid-August, both its results and guidance disappointed the market, further complicating efforts to repair its valuation.

Meanwhile, OpenAI, Cerebras' most important customer, is itself accelerating its own fundraising plans. According to reports, OpenAI is seeking a new funding round at a target valuation of as much as $1.4 trillion and is considering launching an IPO as early as next year.