Horizon3 Secures $250M in Series E Funding, Reaching $2 Billion Valuation Amid Growing AI Threats

Cybersecurity startup Horizon3 has successfully completed a $250 million Series E funding round, leading to a valuation of $2 billion—more than tripling its worth in just 14 months. Based in San Francisco, the company received backing from returning investors such as NightDragon and NEA.

This funding comes amid revelations from two prominent AI research labs indicating that their models unintentionally breached systems beyond their intended targets. Horizon3 has spent six years developing AI specifically designed to probe network vulnerabilities in a safe environment, responding to the growing demand from businesses. As AI-driven attacks increase, companies are rushing to perform comprehensive stress tests on their security measures, a need inadequately served by traditional security vendors.

According to Matt Hartley, the company’s chief revenue officer, its NodeZero platform offers two key benefits: it can assess live systems without disrupting operations—something that many other AI-based tools struggle to do reliably—and it performs ongoing scans across the entire infrastructure, rather than limiting assessments to an annual frequency, thus covering the whole network instead of just 2-3%.

Last year, the company was close to achieving $100 million in annual recurring revenue, growing at a rate of 120% year-over-year, and Hartley expects even faster growth this year.

AI tools have made it easier for attackers to quickly devise new exploits, forcing security teams to react to threats faster than they can manage them. Hartley noted that Horizon3 has invested around $100 million in R&D to create automated systems that remain both predictable and manageable. This investment is particularly significant in light of recent security breaches at AI labs, which have sparked concerns over the containment of AI systems.

“Organizations are becoming increasingly cautious with their AI implementations,” Hartley mentioned. “We are receiving numerous inquiries about the detectability of AI. Yes, we can detect it. However, many companies that rushed to adopt AI are now reconsidering the implications of their decisions, questioning whether their security teams may become overly aggressive, leading to unforeseen complications. As such, organizations are moving into what I would call a bold new world, underscoring the necessity for reliable and consistent testing from a company like Horizon3 to enhance defenses against real-world threats.”

Horizon3 reports having conducted 310,000 production security tests without a single disruption, which they term ‘AI Hackers’, enabling fully autonomous penetration testing.

Hartley emphasized that the main competition does not come from other software vendors; rather, it lies within the existing testing model. While companies collaborating with human security teams for annual assessments will persist, expectations are changing: clients now desire thorough scans of all infrastructure on a monthly or weekly basis instead of just sampling 5% yearly to monitor their safety improvements.

The founders of Horizon3, Snehal Antani and Anthony Pelletier, initially met while serving in Joint Special Operations Command, where they encountered firsthand how resource constraints made continuous security testing difficult. Their mission in founding Horizon3 was to automate these repetitive evaluations.

With this latest funding, Horizon3 is poised for international expansion, planning new offices in Amsterdam (by June 2026), Australia, and Singapore, in addition to establishing a partner network and sustaining substantial R&D investments.

Strategic investors now include Singapore’s EDBI, defense contractor SAIC, and Qualcomm, highlighting the pervasive nature of the vulnerabilities they are addressing across various sectors.

Horizon3 boasts a clientele of approximately 7,200 to 7,300 customers, spanning managed service providers serving small businesses to Fortune 10 corporations. The company estimates its addressable market in the tens of billions of dollars, in line with industry forecasts for the broader cybersecurity sector, which is anticipated to reach $271.9 billion by 2025 and $663.2 billion by 2033, according to Grand View Research.