Corning Stock Plunges 16% as Fiber Growth Slows

Corning , a specialty-materials manufacturer producing optical fiber and advanced glass, plunged more than 16% in Tuesday's premarket trading after issuing a slightly weaker-than-expected third-quarter sales forecast. Corning expects core sales between $4.9 billion and $5 billion and adjusted earnings between $0.85 and $0.89 per share. Those forecasts would still represent year-over-year growth of approximately 16% in sales and 28% in adjusted earnings, but investors appeared focused on slowing expansion in the company's optical-fiber business.

Optical Communications revenue increased 32% to $2.07 billion, compared with growth of 36% in the previous quarter and 81% one year earlier. Corning said demand for products used in generative-AI infrastructure continued accelerating, helping offset more modest performance across other operations. The company has expanded its AI-infrastructure position through partnerships with Amazon.com (AMZN), a cloud-computing and e-commerce company, and NVIDIA (NVDA), an AI-chip designer. Second-quarter revenue reached $4.74 billion, exceeding the $4.61 billion analyst estimate.

Solar-segment sales nearly doubled to $438 million, although the division recorded a quarterly loss following maintenance work and an equipment upgrade. Corning expects that business to become more profitable during the third quarter. The company, which supplies Apple, has also faced weaker global smartphone demand affecting specialty-glass volumes, particularly in display technologies. Corning shares had gained approximately 64% during 2026 after rising 84.2% in 2025, leaving the stock potentially vulnerable to a sharp reaction when the outlook fell below elevated expectations. Investors may now focus on whether accelerating AI demand can offset the deceleration in overall optical-communications growth.