Lumentum Holdings, a leader in photonics and optical technology, will join the Nasdaq-100 Index on May 18, 2026, replacing CoStar Group. This inclusion follows a significant surge in Lumentum's stock, which rose between 145% and 150% in 2026, building on a 339% increase in 2025. The company's market capitalization has reached approximately $70 billion, highlighting its rapid growth and strategic positioning in the semiconductor-adjacent space. Lumentum's success is driven by its specialization in photonic and optical technologies, crucial for high-bandwidth networks needed by hyperscale cloud providers. The company's addition to the Nasdaq-100, announced on May 8, 2026, follows its recent inclusion in the S&P 500, underscoring its expanding market influence. The index change reflects Lumentum's growing prominence, as it now ranks among the largest non-financial companies on the Nasdaq exchange.