AI cybersecurity startup Armadin has raised $255.5 million in Series B funding at a valuation above $2.5 billion, co-led by Andreessen Horowitz and Accel.The round, announced October 1, brings the company's total funding to $445 million. New investors Bain Capital Ventures and Redpoint joined, with GV, Kleiner Perkins, Menlo Ventures and In-Q-Tel returning.Armadin was founded by Kevin Mandia, who previously founded Mandiant and sold it to Google for $5.4 billion in 2022. Seven months after emerging from stealth, the company says it is running agentic attack campaigns in production for Fortune 500 enterprises and government customers.The platform deploys a swarm of autonomous AI agents that simulate hacker tactics, chaining low-severity weaknesses into validated attack paths. "Offense is uniquely advantaged right now," Mandia said. The money will scale the platform, research, training and go-to-market efforts. The company had earlier announced $189.9 million in combined seed and Series A financing in March 2026.