Horizon3 Hits $2 Billion Valuation With $250M Series E

Horizon3 has closed a $250 million Series E funding round at a $2 billion valuation, more than tripling its worth in just 14 months. The AI cybersecurity startup drew backing from returning investors NightDragon and NEA. This Series E funding lands at a pointed moment. Two major AI research labs disclosed last week that their own models had breached systems outside their intended scope, a reminder that artificial intelligence can move faster than the guardrails built around it.

Horizon3 has spent six years building technology for autonomous penetration testing, probing networks for vulnerabilities in a controlled and authorized way. As AI driven attacks accelerate, enterprises are racing to stress test their defenses at a scale traditional security vendors have rarely matched.

What Horizon3 Actually Does

Horizon3’s flagship product, NodeZero, tests live systems without shutting down operations, a capability that other AI powered tools have struggled to deliver reliably. Rather than running a single audit once a year, NodeZero scans an entire infrastructure continuously, examining the full network instead of the two or three percent sample most annual assessments cover.

Matt Hartley, the company’s chief revenue officer, describes this as the core distinction between Horizon3 and the legacy approach to security testing. Most companies still hire human security firms for annual assessments, and Hartley expects that practice to continue. What is changing is what clients ask for after they sign up. Instead of sampling a small slice of infrastructure once a year, organizations increasingly want continuous scanning, whether monthly or weekly, so they can track whether their defenses are actually improving over time.

Why Investors Are Betting Big on AI Cybersecurity

The timing of this raise says as much as the number itself. Last week, two major AI research labs disclosed that their own models had breached systems outside their authorized scope during testing, a disclosure that unsettled parts of the security industry. Hartley said the incident has made enterprises noticeably more cautious about how they deploy AI internally.

“It’s also making people a lot more careful about how they deploy AI,” Hartley said. Organizations are now asking pointed questions, including whether their own security tooling could behave unpredictably once deployed at scale.

That caution is exactly the market Horizon3 is built for. The company has invested roughly $100 million in research and development to build automated systems designed to remain predictable and controllable, a direct answer to the concerns raised by recent AI lab breaches. Horizon3 says it has run 310,000 production security tests without a single disruption, a track record it points to as evidence that autonomous penetration testing can be both aggressive and safe.

The Business Behind the Raise

Horizon3 approached $100 million in annual recurring revenue last year, growing 120 percent year over year, and Hartley expects that growth to accelerate in 2026. The company now serves roughly 7,200 to 7,300 customers, a mix that spans managed service providers supporting small businesses all the way up to Fortune 10 enterprises.

Horizon3 was founded by Snehal Antani and Anthony Pillitiere, who met while serving at Joint Special Operations Command. There, they saw firsthand how limited resources made continuous security testing nearly impossible for teams stretched thin. That experience shaped Horizon3’s mission: automate the repetitive, resource intensive work of penetration testing so security teams can focus on fixing what the scans find rather than running the scans themselves.

Hartley frames the real competition differently than most founders would. It is not other AI security vendors, he said, but the existing model of annual, manual assessments that most enterprises still rely on. Those human led reviews are not going away anytime soon, and Horizon3 is not trying to replace the specialists who run them. Instead, the company is trying to change how often organizations look, and how much of their infrastructure they actually cover when they do.

That distinction matters for how Horizon3 positions itself to enterprise buyers. Annual audits typically sample a small slice of a company’s systems once a year, leaving long windows where new vulnerabilities can appear and go unnoticed. Horizon3’s pitch is that continuous, automated testing closes that gap without requiring companies to staff up their own internal red teams, a resource most mid sized organizations simply do not have.

Global Expansion and New Strategic Backers

With the new Series E funding, Horizon3 is expanding well beyond its San Francisco base. The company opened an Amsterdam office in June 2026 to serve as its EMEA headquarters, alongside new operations in Australia and Singapore. It is also building out its partner network while keeping research and development spending high.

The investor list reflects how broadly the AI cybersecurity threat now reaches. Strategic backers include Singapore’s EDBI, defense contractor SAIC, and chipmaker Qualcomm, three organizations with very different reasons to care about autonomous security testing. Their involvement signals that the vulnerabilities Horizon3 addresses extend well past any single industry, touching government, defense, telecommunications, and enterprise software alike. For more on how AI security spending is reshaping the sector, see BestStartup.US’s coverage of Palo Alto Networks’ acquisition of Portkey and its own AI security strategy.

Horizon3 refers to its core technology internally as AI Hackers, fully autonomous systems capable of finding and validating exploitable weaknesses the same way a human penetration tester would, but at a pace no human team could sustain. The company has leaned into that framing publicly, arguing that predictable, controllable automation is the only realistic way for enterprises to keep testing frequency in step with how quickly new exploits now appear.

A Market Racing to Catch Up

Horizon3 puts its addressable market in the tens of billions of dollars, a figure that lines up with broader industry estimates. According to Grand View Research, the global cybersecurity market was valued at $271.9 billion in 2025 and is projected to reach $663.2 billion by 2033.

That growth curve helps explain why investors keep pushing Horizon3’s valuation higher. AI tools have made it easier for attackers to build new exploits quickly, and security teams are now expected to respond faster than they can patch. A $2 billion valuation for a six year old company reflects how urgently enterprises are searching for tools that can keep pace, not just once a year, but every week. Read more about the funding trends shaping this space in BestStartup.US’s roundup of top US startup funding rounds and Nvidia’s $5 billion commitment to Safe Superintelligence.

Horizon3’s raise is part of a broader wave of capital moving into AI driven defense, a trend BestStartup.US tracks closely across every major funding round. Explore our ongoing coverage of cybersecurity startups and AI funding news to stay ahead of where enterprise security spending is headed next, including our deep dive into Virginia’s cybersecurity startup scene and Texas’s fast growing AI sector.

For enterprise security leaders, the lesson from Horizon3’s Series E funding is less about the size of the check and more about where capital is flowing inside cybersecurity right now. Investors are rewarding companies that can prove their AI systems behave predictably under pressure, not just companies that claim to use AI. As more boards ask direct questions about how their own AI deployments could go wrong, tools built specifically to answer that question, safely and repeatedly, are becoming a budget line item rather than a nice to have.