A chatbot made by Chinese artificial intelligence startup DeepSeek has rocketed to the top of Apple’s App Store charts in the US this week, dethroning OpenAI’s ChatGPT as the most downloaded free app. The eponymous AI assistant is powered by DeepSeek’s open-source models, which the company says can be trained at a fraction of the cost using far fewer chips than the world’s leading models. Shares for Nvidia, the biggest global supplier of advanced AI chips, are currently down over 12…