As 2025 enters its final stretch, large funding rounds are making a comeback. After a slow Thanksgiving week, U.S. startup investments rebounded sharply, with massive late-stage cheques flowing into predictions markets, defense tech, AI infrastructure, cybersecurity and biotech.
This week’s list is led by Kalshi, which officially confirmed its $1 billion mega-round—one of the largest financings in the predictions market space. Other major rounds highlight continued investor demand for AI tools, next-gen defense, molecular biotech, and enterprise infrastructure.
Below is a breakdown of the Top 10 biggest U.S. startup funding rounds announced this week.
1. Kalshi — $1 Billion | Predictions Market
The fast-growing New York-based predictions marketplace confirmed its widely reported $1 billion new funding round. Paradigm led the deal, joined by several major venture firms, reaffirming investor interest in regulated event-based trading.
2. Castelion — $350 Million | Defense Tech
California-based Castelion, a developer of hypersonic munitions founded by SpaceX alumni, raised a massive Series B led by Altimeter Capital and Lightspeed Venture Partners. The startup, founded in 2022, is rapidly emerging as a major player in defense innovation.
3. Eon — $300 Million | Cloud Data Backup for AI
New York’s Eon, a cloud data backup solution built for enterprise AI systems, secured $300 million Series D funding led by Elad Gil (Gil Capital). The round takes Eon’s total funding to $500 million and values the company at $4 billion—impressive for a startup less than two years old.
4. Curative — $150 Million | Health Insurance
Austin-based Curative, known for its zero out-of-pocket healthcare plan, raised $150 million (Series B) led by Upside Vision Fund, pushing its valuation to $1.27 billion.
5. Angle Health — $134 Million | AI Health Benefits
San Francisco’s Angle Health, an AI-first healthcare benefits platform, closed a $134 million Series B led by Portage Ventures. The round combines debt and equity, bringing its total raised capital to nearly $200 million.
6 (Tie). 7AI — $130 Million | Cybersecurity
Boston-based 7AI, which builds AI agents to automate security operations, emerged from stealth just 10 months ago. It has now raised $130 million in Series A, led by Index Ventures, signaling strong early confidence in AI-driven cybersecurity.
6 (Tie). Protego Biopharma — $130 Million | Biotech
San Diego’s Protego Biopharma, developing therapeutics that reprogram protein folding to treat complex diseases, raised $130 million in Series B. The round was co-led by Novartis Venture Fund and Forbion.
8. Triana Biomedicines — $120 Million | Biotech
Lexington-based Triana Biomedicines, maker of a molecular glue discovery platform, secured $120 million Series B led by Ascenta Capital and Bessemer Venture Partners.
9. Antithesis — $105 Million | Simulation Testing
Virginia-based Antithesis, a simulation testing platform for complex software systems, raised a $105 million Series A led by Jane Street Capital.
10. Axiado — $100 Million | AI Server Chips
San Jose’s Axiado, a chipmaker focused on building compact, power-efficient processors for AI servers, secured $100 million Series C+ funding led by Maverick Silicon.
