- Armadin raised $255.5M in a Series B co-led by a16z and Accel.
- The round values the Mandiant founder’s startup at more than $2.5B.
- Armadin’s $445M total tops Horizon3’s $428.5M and XBOW’s $270M-plus.
On August 3, Armadin said it had sent 26,000 AI agents to attack a live institution’s network for three days, with the institution’s consent.
The California startup, founded by Mandiant creator Kevin Mandia, says the swarm chained 38 validated attack paths and produced 238 security findings. On October 1, Armadin raised $255.5 million in a Series B at a valuation above $2.5 billion.
Andreessen Horowitz and Accel co-led the round. Bain Capital Ventures and Redpoint joined as new investors. 8VC, Ballistic Ventures, GV, In-Q-Tel, Kleiner Perkins, and Menlo Ventures also backed it. The round takes Armadin’s total funding to $445 million, including the $189.9 million of combined seed and Series A money it announced on March 10.
It will spend the new capital on its platform, research, training, and getting the product to customers. The announcement gives no revenue figure and names no customer.
“Offense is uniquely advantaged right now. AI lets an attacker find and chain weaknesses faster than any human team can respond. The only way to build a defense that keeps pace is to train it against the best offense available, every day. That is what we built. With a16z and Accel co-leading and the support of every investor in this round, we are going to put that offense to work for the enterprises and government agencies defending the world’s most critical systems,” said Mandia, Armadin’s CEO.
A cap table built around the founder
Mandia founded Mandiant in 2004 and sold it to Google in a $5.4 billion deal announced in 2022. He started Armadin in September 2025 with chief technology officer Travis Lanham, chief offensive security officer Evan Peña, and chief architect David Slater. By the March launch, the company had hired more than 60 people, CNBC reported.
Mandia also co-founded Ballistic Ventures, which led Armadin’s seed round and returned for the Series B. On September 8, he joined Amazon’s board and was named to its audit and security committees. The biggest change on the cap table is a16z, which was not named in the seed and Series A announcements.
“Against agentic adversaries, the best defense is a great offense powered by AI. That was our conviction when we led Armadin’s Series A, and it’s even more pressing today. In less than a year, Armadin has set the standard for AI-powered offensive security and remediation across enterprises and governments, and we’re excited to keep partnering with them,” said Ping Li, a partner at Accel who invests in cybersecurity.
“Every major platform shift creates a new generation of security leaders, and AI is the biggest shift we’ve seen. Kevin has been on the front lines of the most consequential breaches in history, and he has built a team that pairs elite red teamers with world-class AI engineers,” added David George, a general partner at a16z who heads its growth fund.
Money is plentiful on this cap table. Since March, four of Armadin’s backers have closed new funds: Kleiner Perkins with $3.5 billion, Menlo Ventures with $3 billion,Accel with $3.5 billion, and Bain Capital Ventures with $1.6 billion.
An autonomous swarm of hackers
Companies usually test their defences with penetration tests, where hired hackers probe their systems at set intervals. Armadin argues that periodic checks cannot keep up with attackers who use AI to search for weaknesses around the clock.
The startup deploys a swarm of specialised AI agents that reason like an attacker across a company’s systems. Weaknesses that look minor alone get chained into one validated path, for example, from running commands on an exposed server without logging in, through hopping between internal systems, to full compromise of a cloud environment.
The obvious risk is control. OpenAI said in July that its own models escaped a test environment and reached Hugging Face’s systems, CNBC reported. Tech Funding News has since covered startups such as Kontext that build guardrails for AI agents. Armadin says each of its agents runs in a locked-down sandbox, every action passes through a filter coded to block anything out of scope, and agent behaviour is watched in real time. On September 28, it said it was contributing to NVIDIA’s open-source OpenShell software, which draws a boundary around what agents can do.
The autonomous cybersecurity race
Armadin is not alone. Seattle-based XBOW raised $120 million in a Series C on March 18 at a valuation above $1 billion. In May, it added $35 million from strategic backers including NVIDIA’s NVentures, Samsung Ventures, Accenture Ventures, and SentinelOne’s S Ventures. That took the round to $155 million and XBOW’s total funding past $270 million. San Francisco-based Horizon3, maker of the NodeZero testing tool, raised $250 million at a valuation above $2 billion on August 3, triple the $650 million it was worth in June 2025. Its total funding stands at $428.5 million.
By TFN‘s count, those three rounds total $ 660.5 million announced between March 18 and October 1. Armadin’s $445 million total already exceeds both rivals’ totals, about 13 months after Mandia founded it. In Europe, Amsterdam-based Hadrian was an early entrant, with a seed round of about €10 million in June 2022 after a €2.5 million pre-seed in 2021.
Investors have valued a company about 13 months old at over $2.5 billion. That price assumes Armadin can turn a one-off spectacle into software customers renew, and keep its agents inside the lines on other people’s networks.
