Horizon3 Raises $250M Series E at $2B+ Valuation to Lead the ‘AI vs. AI’ Security Era

Cyberattacks now move at the speed of AI, and traditional, human-paced defenses are struggling to keep up. As attackers increasingly wield AI of their own, the industry has entered what some call an “AI vs. AI” era — one in which defenders must fight machines with machines.

Horizon3, an AI-native proactive security company based in San Francisco, is betting that the best defense is a good offense. Its flagship platform, NodeZero, is an autonomous penetration-testing tool that safely attacks an organization’s own production environment. It shows exactly how an adversary would chain together misconfigurations, weak credentials, and identity gaps to compromise critical systems, offers fix guidance, and then instantly verifies that the remediation worked. As it tests, NodeZero can also plant honeypots to catch AI attackers already inside the network.

That “attack, fix, verify” loop has driven 120% year-over-year ARR growth. Horizon3 now protects more than 7,000 organizations worldwide, including multinational banks, major healthcare networks, and four Fortune 10 enterprises. The company is FedRAMP High authorized and says it has safely executed 310,000 tests in production environments — the “data moat” it credits for its results.

Horizon3 was founded in 2019 by CEO Snehal Antani and a team of technology and military veterans. Antani previously served as the first CTO of the U.S. military’s Joint Special Operations Command (JSOC), and before that as CTO and SVP at Splunk and CIO at GE Capital, beginning his career as a software engineer at IBM.

The company announced a $250 million Series E co-led by existing investors NightDragon and NEA. The oversubscribed round drew seven new investors — including Acrew Capital, Sapphire Ventures, Singapore’s EDBI, and SAIC — alongside returning backers such as Craft Ventures and Qualcomm Ventures. The round values Horizon3 at more than $2 billion, roughly triple its $650 million valuation at Series D just over a year ago.

As part of the deal, Dave DeWalt — founder of NightDragon and former CEO of FireEye and McAfee — and NightDragon managing director Morgan Kyauk will join Horizon3’s board. The company plans to use the capital to scale its go-to-market operations, expand into Singapore, Australia, and across EMEA, and build a continuous learning loop between AI attackers and AI defenders, including new autonomous “blue-team” agents that remediate findings directly from NodeZero pentests.

A crowded ‘AI vs. AI’ security market

Capital is pouring into cybersecurity as AI automates both attack and defense. In the offensive, autonomous-pentesting niche where Horizon3 operates, rivals include XBOW and Pentera. On the defensive side, security-automation firm Torq reached unicorn status on a $140 million round, while others race to embed AI across detection, endpoint, and identity. The common thread: as vulnerabilities multiply, the winners will be those that can not just find exploitable problems, but fix them at machine speed.