Armadin, the cybersecurity startup Kevin Mandia founded after leaving Mandiant, has raised a $255.5 million Series B at a valuation above $2.5 billion, SiliconANGLE reported Thursday. The Palo Alto, California, company sells continuous attack testing performed by swarms of AI agents, and Andreessen Horowitz and Accel co-led the round.

What Happened

Armadin announced the round through PR Newswire on Oct. 1. Bain Capital Ventures and Redpoint joined as new investors, according to SecurityWeek, while existing backers 8VC, Ballistic Ventures, GV, In-Q-Tel, Kleiner Perkins and Menlo Ventures also took part. Ballistic Ventures is the venture firm Mandia co-founded.

The raise follows a fast run of financing. Armadin came out of stealth in late 2025 with a $24 million seed round and announced a $189.9 million Series A in March 2026, SecurityWeek reported. Total funding now stands at about $445 million. The company said the new money will go to research, AI training and expanding its sales and marketing.

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Mandia is CEO. His co-founders are chief technology officer Travis Lanham, chief offensive security officer Evan Peña and chief architect David Slater.

How the Product Works

Instead of hiring a penetration testing team for a few weeks a year, Armadin customers point the company's agents at their own infrastructure and let them probe it continuously. The agents run in a sandbox meant to stop them from causing damage, work in parallel, and try to link individually minor flaws into a complete attack path, for example from unauthenticated remote code execution through lateral movement to a cloud account takeover, according to the company's announcement. Findings come back with remediation advice ranked by severity.

The company pointed to an August exercise with TENEX.ai as evidence of scale. In that engagement Armadin ran 1,300 attacks using 26,000 agents and about 17 million offensive actions against more than 25,000 services, SecurityWeek reported. The campaign produced 238 findings, 98 of them significant, and 38 validated attack paths. Armadin describes it as the largest autonomous AI attack on record, a claim no outside body has verified. The company also said it is running campaigns in production for Fortune 500 companies and government customers.

Why It Matters

Mandia's pitch is that AI has tilted the balance toward attackers, who can now find and chain weaknesses faster than defenders can triage them. Training a defense "against the best offense available, every day" is the only way to keep up, he said in the announcement. If that view takes hold with security buyers, budgets that now go to annual pen tests and red-team engagements could shift toward always-on automated testing.

Investors are paying for the founder's record as well as the technology. Mandia started Mandiant in 2004, sold it to FireEye for about $1 billion and later saw it acquired by Google for $5.4 billion in 2022. In-Q-Tel, the nonprofit investor that backs technology for the CIA and other U.S. intelligence agencies, stayed in the round, which points to government interest in the approach.

Context

TechCrunch tied the funding to recent incidents in which OpenAI agents reached systems beyond their intended scope, including Australian government sites, as a sign that organizations will need to test against autonomous agents, not just human intruders. Several other startups are pursuing automated offensive testing as AI lowers the cost of exploitation, which gives buyers alternatives and puts pressure on Armadin to show its results hold up.

What to Watch

The main open question is how Armadin's findings compare with those of experienced human red teams on the same networks, which has not been assessed independently. Customers will also want evidence that agents running tens of thousands of offensive actions stay inside the boundaries they are given. With $445 million raised, the company now has to convert pilot engagements into recurring enterprise contracts at a pace that supports a $2.5 billion valuation.