Horizon3 Reaches $2 Billion Valuation After $250 Million Series E Funding Round

Cybersecurity startup Horizon3 has secured $250 million in a Series E funding round, pushing its valuation to $2 billion as organisations increase spending on defences against rapidly evolving AI-driven cyber threats. The San Francisco-based company said the latest investment more than triples its valuation from 14 months ago and was led by returning investors NightDragon and NEA.

The funding comes at a time when artificial intelligence is reshaping both cyberattacks and cyber defence. Last week, two major AI research labs disclosed incidents in which their AI models breached systems beyond their intended scope, adding to concerns about how advanced AI systems are deployed and controlled inside organisations.

Horizon3 has spent the past six years developing AI designed specifically for authorised penetration testing rather than offensive cyberattacks. The company’s NodeZero platform automatically probes enterprise networks to identify exploitable weaknesses, helping organisations test their security posture continuously without disrupting business operations.

Demand grows for continuous AI-powered security testing.

Chief Revenue Officer Matt Hartley said NodeZero differs from many security testing tools because it can safely examine production environments without forcing organisations to shut down systems. He added that the platform continuously evaluates an organisation’s entire infrastructure instead of relying on annual penetration tests that typically review only a small portion of enterprise networks.

According to Hartley, Horizon3 approached $100 million in annual recurring revenue last year while delivering 120% year-over-year growth. The company expects that growth to accelerate as businesses seek more frequent security assessments to keep pace with AI-powered threats.

Hartley said generative AI has dramatically reduced the time attackers need to develop new exploits, leaving security teams under pressure to identify and remediate vulnerabilities faster than ever. To address that challenge, Horizon3 has invested roughly $100 million in research and development to build AI systems designed to remain predictable, controllable and suitable for enterprise security testing.

AI adoption brings new security questions.

Recent incidents involving AI models escaping their intended operating boundaries have also changed how organisations think about deploying AI internally. Hartley said customers increasingly ask whether Horizon3 can identify AI systems operating inside enterprise environments, but the broader concern is ensuring that AI deployments do not introduce unintended security risks.

“It’s also making people a lot more careful about how they deploy AI,” Hartley said. He added that many organisations that previously rushed to introduce AI tools are now reassessing the potential consequences of those deployments and looking for consistent, repeatable methods of validating their defences.

In a company statement, Horizon3 said it has completed more than 310,000 production security tests without disrupting customer operations. The company describes its approach as “I Hackers,” referring to fully autonomous penetration testing designed to simulate real-world attack techniques under authorised conditions.

Replacing infrequent testing with continuous assessments

Hartley said Horizon3’s biggest competition is not another cybersecurity vendor but the traditional model of hiring external consultants to perform penetration tests once a year. While those services continue to play an important role, customers increasingly want security assessments that occur monthly or even weekly instead of relying on periodic snapshots of their environments.

Rather than examining only a small percentage of enterprise infrastructure, organisations are asking for continuous visibility across their complete networks so they can measure whether their security posture is improving over time.

Expansion follows strong customer growth.

Horizon3 was founded by Snehal Antani and Anthony Pillitiere, who met while serving at Joint Special Operations Command. Their experience highlighted how resource limitations made continuous cybersecurity testing difficult, leading them to develop an automated platform capable of performing repetitive security assessments at scale.

The new funding will support thecompany’ss international expansion, including recently established operations in Amsterdam and additional growth in Australia and Singapore. Horizon3 also plans to expand its partner ecosystem while continuing significant investment in research and development.

Strategic investors now include Singapore’s EDBI, defence contractor SAIC and Qualcomm, reflecting interest in the company’s technology across government, defence and commercial sectors.

According to the company, Horizon3 serves approximately 7,200 to 7,300 customers ranging from managed service providers supporting small businesses to Fortune 10 enterprises. The company believes its opportunity spans a market worth tens of billions of dollars, against the backdrop of a global cybersecurity industry that Grand View Research valued at $271.9 billion in 2025 and projects will grow to $663.2 billion by 2033.