Cybersecurity startup Horizon3 has raised a $250 million Series E at a $2 billion valuation, more than tripling its valuation in 14 months. The San Francisco-based firm drew backing from returning investors NightDragon and NEA.

The funding arrives as two major AI research labs disclosed last week that their models had breached systems outside their intended scope. Horizon3, which has spent six years building AI specifically designed to probe networks for vulnerabilities in a controlled, authorized manner, is riding growing enterprise demand. With AI-driven attacks accelerating, enterprises are rushing to stress-test their defenses at scale, a gap that traditional security vendors have largely left unfilled.

Matt Hartley, the company’s chief revenue officer, said that its NodeZero platform has two core strengths: It can test live systems without shutting down operations, a capability other AI-powered tools have struggled to deliver reliably, and it scans an entire infrastructure continuously rather than once a year, examining the full network rather than just 2-3%.

The company approached $100 million in annual recurring revenue last year with 120% year-over-year growth,and expects to accelerate growth this year, Hartley said.

AI tools have made it easier for attackers to develop new exploits quickly, forcing security teams to handle threats faster than they can fix them. Horizon3 spent roughly $100 million in R&D building automated systems designed to stay predictable and controllable, Hartley said. That’s significant given recent breaches at AI labs, which raised questions about whether any AI system can truly remain contained.

“It’s also making people a lot more careful about how they deploy AI,” Hartley said. “We’re getting a lot of questions today around: can you detect AI? Of course we can. But I think a lot of organizations that rushed to deploy AI across the enterprise are now thinking twice about the ramifications of those deployments; what if my own security team gets too aggressive, could there be unintended consequences? So a lot of organizations are moving into what I’d call a bold new world, which is exactly why you need consistent, predictable testing from a company like Horizon3, to know how to strengthen your own defenses against real-world exploits.”

In a statement, Horizon3 has run 310,000 production security tests with zero disruptions, establishing what it calls ‘AI Hackers’, fully autonomous penetration testing.

The real competition isn’t other software vendors; it’s the existing model, according to Hartley. Most companies hire human security firms to run annual tests and those won’t disappear, he continued. What’s shifting is what clients demand after signing up: Instead of sampling 5% of infrastructure once yearly, they now want to scan everything monthly or weekly, tracking whether they’re actually getting safer.

Horizon3’s founders, Snehal Antani and Anthony Pelletier, met while serving at Joint Special Operations Command, where they saw firsthand how resource constraints made continuous security testing difficult. They founded Horizon3 to automate those repetitive assessments.

With the funding, Horizon3 is expanding internationally,including new offices in Amsterdam (in June 2026), Australia, and Singapore, while building a partner network and maintaining substantial R&D spending.  

Strategic investors now include Singapore’s EDBI, defense contractor SAIC, and Qualcomm, signaling that the vulnerability they’re addressing extends well beyond any single sector.

Horizon3 has roughly 7,200 to 7,300 customers, ranging from managed service providers serving small businesses to Fortune 10 enterprises. The company claims an addressable market of tens of billions of dollars, a figure that aligns with industry estimates of the broader cybersecurity market, valued at $271.9 billion in 2025 and projected to reach $663.2 billion by 2033, according to Grand View Research.