Why is Cerebras Systems stock sliding today?

Cerebras Systems stock experienced a significant 6.3% decline in early trading after a statement from SemiAnalysis on X revealed that OpenAI's latest model, GPT-6.1 Sol Ultrafast, is not running on Cerebras hardware. Instead, it appears to be utilizing Nvidia GPUs, potentially Blackwell-class chips like the GB300, at a low batch size.

This news has raised concerns among analysts about the company's ability to maintain its pivotal role in powering the GPT-6.1 Sol Ultrafast tier. OpenAI initially announced in August that Cerebras would facilitate the Ultrafast tier for GPT-5.6 Sol, achieving up to 750 tokens per second, which served as a significant validation of the Wafer-Scale Engine architecture.

However, GPT-6.1 Sol Ultrafast, revealed at OpenAI's DevDay on September 29, only reaches around 300 tokens per second, casting doubt on whether the larger model's scale can fully leverage Cerebras' on-chip memory capabilities. Additionally, Cerebras faces other challenges, including a GAAP net loss of $450.5 million in its latest quarter and insider share sales amounting to roughly $266 million over the past three months.

The broader market also had minimal impact on the decline, with both the S&P 500 and Nasdaq trading higher on the day, with the Nasdaq up 0.9%. Consequently, Cerebras finds itself among the most underperforming semiconductor stocks in the session. The company's shares are now approaching their 52-week low of $160.81, falling short of their 52-week high of $386.34, indicating ongoing valuation pressures since the IPO earlier this year.

As the hardware arrangement for GPT-6.1 Sol Ultrafast remains uncertain until further clarification from Cerebras or OpenAI, this uncertainty is expected to continue pressuring the stock's performance.