The Horizon3 Series E round has landed at $250 million, pushing the San Francisco cybersecurity firm to a $2 billion valuation, more than triple where it stood just 14 months ago. The timing is pointed: two major AI research labs disclosed last week that their models had breached systems outside their intended scope, which is roughly the best possible backdrop for a company that sells automated network penetration testing.
The round was led by returning investors NightDragon and NEA. New participants, as reported by The CyberWire, included Acrew Capital, Blue Cloud Ventures, Demeter Group, PSG, and Sapphire Ventures, alongside returning backers Craft Ventures, Prosperity7 Ventures, Qualcomm Ventures, Ridge Ventures, and SignalFire. Strategic names on the cap table, including Singapore’s EDBI, defence contractor SAIC, and Qualcomm, signal that the vulnerability-detection problem Horizon3 is solving cuts across sectors well beyond tech.
What the Horizon3 Series E Funding Pays For
International expansion is already under way, with new offices planned in Amsterdam (opening June 2026), Australia, and Singapore. Beyond that, Horizon3’s own press release confirms a separate $20 million investment in its global partner ecosystem, announced on 5 August 2026. The programme is led by Tim Mackie, Vice President of Global Channels and Alliances, who described the commitment as designed to ensure partners can ‘deliver security their customers can prove, at the speed and scale the market demands.’ Recent partnerships named include World Wide Technology and Brinqa, extending the platform into exposure management and remediation orchestration.
Substantial R&D spending is also being maintained. The company says it has already sunk roughly $100 million into building automated systems engineered to stay predictable and controllable, a design choice that looks less like boasting and more like a direct response to the containment failures now surfacing at AI labs.
The Market Problem Horizon3 Is Betting On
Chief revenue officer Matt Hartley frames the competitive picture plainly: the real opposition is not rival software vendors, it is the incumbent model of hiring human security firms to run annual penetration tests. Those engagements typically sample around 2 to 3 per cent of infrastructure, once a year. Horizon3’s NodeZero platform, by contrast, runs continuously across the full network without taking live systems offline, a capability Hartley says other AI-powered tools have struggled to deliver reliably.
Enterprises are starting to demand something closer to continuous proof that their posture is improving, rather than a once-yearly snapshot. Hartley puts it directly: ‘A lot of organisations 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 organisations 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 defences against real-world exploits.’
Horizon3 claims it has run 310,000 production security tests with zero disruptions, the metric it uses to market what it calls ‘AI Hackers’, its fully autonomous penetration testing offering.
The business appears to be growing into that pitch. The company approached $100 million in annual recurring revenue last year, with 120% year-over-year growth, and Hartley says it expects to accelerate further this year. The customer base sits at roughly 7,200 to 7,300 organisations, ranging from managed service providers serving small businesses up to Fortune 10 enterprises.
Founders Snehal Antani and Anthony Pillitiere met at Joint Special Operations Command, where resource constraints made continuous security testing impractical. That experience shaped the product thesis: automate the repetitive assessments that human teams cannot run at scale or frequency.
Horizon3’s LinkedIn page lists rankings that add context to the growth story: the firm placed third overall on the 2025 Deloitte Technology Fast 500 and topped the Inc. 5000’s cybersecurity category the same year. Those figures come from an aggregator source, so treat them as directional rather than audited, but the trajectory they describe aligns with the ARR and growth rate figures Hartley has stated publicly.
The broader market Horizon3 is targeting is large enough that even a small share justifies the valuation arithmetic. Grand View Research values the global cybersecurity market at $271.9 billion in 2025 and projects it will reach $663.2 billion by 2033. Horizon3’s claimed addressable market of tens of billions sits comfortably inside those numbers.
The Horizon3 Series E lands at a moment when AI containment failures are no longer theoretical. If the next lab breach makes the evening news, the pipeline for automated security testing probably gets a lot shorter. Horizon3 is positioned to benefit, as long as its own AI stays on the right side of the fence.
