Horizon3 Raises $250M on One Bet: AI Will Attack, So AI Must Defend

The cybersecurity industry spent decades hiring humans to hack systems and write reports. Horizon3 is replacing that with a machine that never sleeps.

The San Francisco-based company has raised a $250 million Series E at a valuation exceeding $2 billion, co-led by existing investors NightDragon and NEA. Seven new investors joined the round including Acrew Capital, EDBI from Singapore, PSG, SAIC, and Sapphire Ventures. The round was oversubscribed.

Horizon3 builds NodeZero, an autonomous penetration testing platform that safely operates inside live production environments. Banks, hospitals, and government agencies use it to find their own vulnerabilities the way an attacker would — continuously, not once a year during an audit. The company currently protects more than 7,200 organizations globally and is approaching $100 million in annual recurring revenue, growing at 120% year over year.

The framing the company is using for this raise is deliberate: "AI vs. AI." The argument is that AI-powered attacks are now generating exploits faster than any human red team can respond to. The only counter is an AI that runs the same playbook on defense, autonomously, all the time.

The new capital will fund expansion into Singapore, Australia, and deeper presence across Europe, the Middle East, and Africa.

What this means for founders

The cybersecurity market is bifurcating between companies that automate human tasks and companies that replace entire human-led workflows with autonomous systems. Horizon3 is the latter. For founders in security, this round draws a clear line: products that assist human analysts are one category, products that run the entire attack-and-defense cycle autonomously are another. The $2 billion valuation tells you which category the market is currently rewarding.

Investors: NightDragon, NEA, Acrew Capital, EDBI, PSG, SAIC, Sapphire Ventures Round: Series E — $250MValuation: $2 billion+