Armadin, the AI-native cybersecurity company founded by former Mandiant CEO Kevin Mandia, closed a $255.5 million Series B on Oct. 1, 2026, at a $2.5 billion valuation.

Andreessen Horowitz and Accel co-led the round. Bain Capital Ventures and Redpoint joined as new investors; returning backers included 8VC, Ballistic Ventures, Google Ventures, In-Q-Tel, Kleiner Perkins, and Menlo Ventures.

The capital brings Armadin's total funding to more than $445 million—a six-month follow-on to its $190 million Series A in March 2026. The company emerged from stealth seven months before the Series B close.

Armadin's core product deploys swarms of autonomous agents to simulate adversary behavior across an organization's attack surface. Unlike traditional penetration tests conducted by human teams on periodic schedules, the agents identify and chain low-severity vulnerabilities into validated kill chains that reveal realistic exploit paths from perimeter to cloud compromise. Security teams can then sever these attack paths before exploitation occurs.

"Offense is uniquely advantaged right now," Mandia said. "AI lets an attacker find and chain weaknesses faster than any human team can respond." Traditional scanners fail by scoring vulnerabilities in isolation, missing how weaknesses connect to form exploitable sequences—a gap Armadin's agent-driven testing closes.

The startup counts Fortune 500 enterprises and government customers running agentic attack campaigns in production today. Capital will fund platform scaling, research expansion, training programs, and go-to-market acceleration.

Ping Li, a partner at Accel, noted the firm led the Series A based on conviction that AI-powered offense is the best defense against agentic adversaries. "Armadin has established the standard for AI-powered offensive security and remediation for enterprises and governments in less than a year," Li said.

Andreessen Horowitz general partner David George framed the moment as a generational shift: major platform transitions spawn new security leaders, and AI represents the largest shift yet. "Mandia has been at the forefront of significant breaches and has built a team combining elite red teamers with world-class AI engineers," George said.

Mandia sold his previous cybersecurity startup Mandiant to Google for $5.4 billion in 2022.