The Week’s 10 Biggest Funding Rounds: Safe Superintelligence And Commonwealth Fusion Lead With Billion-Dollar Deals

Want to keep track of the largest startup funding deals in 2026 with our curated list of $100 million-plus venture deals to U.S.-based companies? Check out The Crunchbase Megadeals Board . This is a weekly feature that runs down the week’s top 10 announced funding rounds in the U.S. Check out last week’s biggest funding deal roundup here . Another week, another bevy of big rounds. For this past week, the largest round was a reported $5 billion Nvidia -backed financing for foundational AI unicorn Safe Superintelligence , followed by a $1 billion investment in Commonwealth Fusion Systems . Other sizable rounds went to companies in sectors including energy storage, health testing, nuclear power, fintech, and, yes, AI. 1. Safe Superintelligence , $5B, foundational AI: AI lab Safe Superintelligence announced a long-term partnership with Nvidia to rapidly accelerate its growth. The deal reportedly included a $5 billion investment from the chip giant with an eye toward boosting compute resources for Safe Superintelligence, a Silicon Valley startup founded by OpenAI co-founder Ilya Sutskever . 2. Commonwealth Fusion Systems , $1 billion, fusion energy: Commonwealth Fusion Systems, a startup working on fusion energy technology and developing a grid-scale fusion power plant, raised $1 billion in fresh funding from unspecified investors. The round brings the total invested to date for the Massachusetts-based company to $4 billion. 3. Antora Energy , $550M, thermal energy storage: Antora Energy, a company that provides energy through thermal batteries to data centers, announced that it has closed on $550 million in a Series C funding round. G2 Venture Partners and Eclipse co-led the financing for the nine-year-old, San Jose-based company. 4. Function , $450M, health testing: Austin-based Function, a provider of lab testing, imaging, and personal health information that markets to consumers, secured $450 million in growth financing from General Catalyst . 5. Antares , $370M, nuclear energy: Antares, a nuclear fission energy company that develops compact microreactors for defense and space applications, raised $370 million in Series C equity funding. Paradigm and Caffeinated Capital led the financing for the three-year-old company, which raised $100 million in debt funding alongside the equity investment. 6. Simile , $200M, AI simulation: Simile, a developer of AI tools for running simulations, said it picked up over $200 million in fresh funding at a $2 billion post-money valuation. Greenoaks led the round, which comes just five months after the Palo Alto-based company launched its product. 7. ThreatLocker , $190M, cybersecurity: Cybersecurity provider ThreatLocker closed on $190 million in Series F funding to hone its platform and expand internationally. Elephant led the round for the Orlando-based company. 8. CAIS , $170M, fintech: New York-based CAIS, an alternative investment platform for independent financial advisors, secured $170 million in Series D financing. Vista Equity Partners led the round, which set a valuation for the company of more than $2 billion. 9. PEX , $160M, fintech: PEX, an AI-enabled provider of prepaid and charge cards for businesses, along with tools to track finances, raised $160 in equity and debt funding, with Bluff Point Associates as lead investor. 10. Eliyan , $145M, AI infrastructure: Eliyan, a developer of connectivity technology for AI infrastructure, completed its Series C with a total of $145 million at a $1 billion valuation. Seligman Ventures led the financing for the five-year-old Santa Clara, California-based company. Illustration: Dom Guzman