US stock indices closed mixed on Monday as chipmakers extended their selloff ahead of this week's Fed decision and a busy slate of economic data and corporate earnings. The S&P 500 ended little changed, the Nasdaq 100 lost 0.3%, while the Dow gained 263 points. Nvidia fell 5% after announcing a $500 billion AI memory chip supply agreement with SK Hynix. Separately, the company guaranteed $250 billion for OpenAI to lease computing capacity from a major data center project, reviving concerns that circular AI financing deals could unravel if hyperscalers curb capital spending. Micron (-2.2%), AMD (-5.2%), Intel (-0.7%), and Sandisk (-11%) also declined. Meanwhile, easing concerns over tight financial conditions helped the Dow. The US and Iran paused strikes over the weekend, sending oil prices and Treasury yields lower, easing expectations of a Fed rate hike this week. Apple (+1.2%), Meta (-0.2%), Amazon (-0.3%), and Microsoft (+1.9%) traded mixed ahead of earnings releases.