Check out the companies making headlines in premarket trading. Nvidia — The artificial intelligence darling saw shares tumbling more than 11% in premarket trading, on track for its worst day since March 2020. The sell-off occured after Chinese startup DeepSeek launched a free open-source large-language model in late December, saying it was developed in just two months at a cost of under $6 million. The move called into question the need for Nvidia’s fastest chips and its competitiveness. Other chipmakers also declined, with Broadcom losing 12% and AMD shedding 4%. Microsoft , Amazon — Other megacap stocks also sold off sharply after the news of DeepSeek stoked questions about the large amounts of money big tech companies have been investing in AI models and data centers. Shares of Microsoft shed 5%, while Amazon dropped by more than 4% and Meta Platforms slid by 2.5%. Vertiv Holdings — Shares of the datacenter services company tumbled 16% as the artificial intelligence trade in the U.S. reversed. If the emergence of DeepSeek leads to less AI infrastructure spending than expected in the future, that could hurt Vertiv’s business outlook. Constellation Energy , Vistra — Power providers for AI infrastructure were also hit hard on concerns that there would be less energy needed if Deepseek can perform using fewer chips. Constellation Energy, Vistra, Nuscale Power and Oklo all slid at least 10% in premarket trading. AT & T — The telecommunications giant added 2.3% after earnings for the fourth quarter came in higher than Wall Street expected. The company earned 54 cents per share, excluding items, exceeding the consensus forecast of analysts polled by StreetAccount by 4 cents. AT & T also posted $32.3 billion in revenue, while analysts expected $32.02 billion. D.R. Horton – Shares of the homebuilding company fell nearly 1% after receiving a downgrade to neutral from buy at Bank of America. The bank said a “challenging” housing market backdrop and rising input costs could weigh on the company from here. – CNBC’s Alex Harring, Sean Conlon and Jesse Pound contributed reporting.