This past week’s largest U.S. startup funding rounds were led by Safe Superintelligence and Commonwealth Fusion Systems. Safe Superintelligence, a foundational AI lab founded by OpenAI co-founder Ilya Sutskever, announced a long-term partnership with Nvidia that reportedly included a $5 billion investment to boost compute resources. Commonwealth Fusion Systems, a Massachusetts-based fusion energy startup, raised $1 billion in fresh funding from unspecified investors, bringing its total invested to date to $4 billion. Antora Energy, a San Jose-based thermal energy storage company, closed on $550 million in a Series C round co-led by G2 Venture Partners and Eclipse. Austin-based health testing provider Function secured $450 million in growth financing from General Catalyst. Antares, a nuclear fission energy company developing microreactors, raised $370 million in Series C equity funding led by Paradigm and Caffeinated Capital, alongside $100 million in debt funding. Simile, a Palo Alto-based AI simulation developer, picked up over $200 million at a $2 billion post-money valuation, led by Greenoaks. Cybersecurity provider ThreatLocker closed on $190 million in Series F funding led by Elephant. New York-based fintech CAIS secured $170 million in Series D financing led by Vista.