The first month of 2026 is drawing to a close, and a cluster of U.S. stocks has just posted their best, or worst, monthly performances on record, driven by a powerful mix of earnings surprises, guidance updated and AI-related sector disruptions.

January's Most Extreme Stock Gainers: Who Just Logged A Best Month Ever?

On the upside, Sandisk Corp. (NASDAQ:SNDK) stood out as one of January's biggest winners, surging more than 150% during the month as the company reported exceptional quarterly earnings that crushed Wall Street expectations.

The rally was fueled by tightening memory and storage supply conditions, as booming AI data-center demand continues to strain capacity.

January also marked Sandisk's best-performing month since its IPO in February 2025. The stock is now up more than 1,400% since going public and was the top-performing S&P 500 constituent for the month.

Cameco Corp. (NYSE:CCJ) advanced 37%, supported by a series of analyst upgrades to earnings forecasts and price targets as expectations for long-term nuclear demand strengthened.

Rising uranium prices and renewed policy support for nuclear energy have reinforced the company's growth outlook.

Defense giant Lockheed Martin Corp.