Shares of Cerebras Systems dropped 8.0% in morning trading on Monday, reaching a new 52-week low of $148.50. The AI chipmaker faces pressure from concerns about its relationship with OpenAI and an approaching lockup expiration.

The decline follows an industry report from late September indicating that OpenAI's GPT-6.1 Sol "Ultrafast" inference tier operates on Nvidia GPUs instead of Cerebras hardware. OpenAI represents one of Cerebras' most important customers and is connected to a multi-year, multi-billion-dollar compute agreement.

The stock also faces selling pressure ahead of a lockup expiration scheduled for around October 14, 2026. Approximately 19.4 million shares will become eligible for sale as part of a staggered post-IPO unlock schedule.

A Form 4 filing dated October 7 showed continued insider activity. Previous executive share sales, including a large transaction by the company's chief operating officer in late September, have created expectations of additional selling around each unlock date.