Horizon3 secures $250 million to scale autonomous security testing
Cybersecurity startup Horizon3 has raised a $250 million Series E at a $2 billion valuation, more than tripling its valuation in 14 months. Returning investors NightDragon and NEA backed the San Francisco company as enterprises increase their demand for frequent, large-scale security testing.
The financing follows disclosures by two major AI research labs that their models had breached systems outside their intended scope. Horizon3 has spent six years developing AI that probes networks for vulnerabilities in a controlled and authorized manner.
Continuous testing of live infrastructure
Chief revenue officer Matt Hartley identified two central strengths of Horizon3's NodeZero platform. It can test live systems without shutting down operations, and it continuously scans an organization's entire infrastructure rather than assessing only a small sample once a year.
Horizon3 says it has conducted 310,000 production security tests with zero disruptions. It describes NodeZero's fully autonomous penetration-testing capability as “AI Hackers.” The company spent roughly $100 million on research and development to make its automated systems predictable and controllable, Hartley said.
That focus reflects a practical challenge for security teams. AI tools allow attackers to develop exploits more quickly, increasing the pressure on defenders to identify and address weaknesses. Questions about containment have also made organizations more cautious about deploying AI throughout their operations.
A challenge to the annual assessment model
Hartley said Horizon3's main competition is not another software vendor but the established practice of hiring human security firms for annual tests. Those services are not expected to disappear, but clients increasingly want to examine all infrastructure monthly or weekly and measure whether their security is improving.
The shift sits alongside enterprise AI agents independent of frontier labs, which illustrates broader enterprise demand for AI systems designed to operate with greater control and less dependence on frontier laboratories.
Horizon3 approached $100 million in annual recurring revenue last year after 120% year-over-year growth and expects growth to accelerate this year, Hartley said. It serves roughly 7,200 to 7,300 customers, from managed service providers supporting small businesses to Fortune 10 enterprises.
Expansion backed by strategic investors
Founders Snehal Antani and Anthony Pelletier met at Joint Special Operations Command. There, the NSA conducted annual security assessments but lacked the personnel to provide monthly follow-ups. The pair created Horizon3 to automate the work that military testing partners could not staff.
The new capital will support international expansion, a partner network and continued R&D spending. Horizon3 plans offices in Amsterdam in June 2026, Australia and Singapore. Strategic investors include Singapore's EDBI, defense contractor SAIC and Qualcomm.
For businesses, the practical implication is that an annual sample may no longer provide enough visibility into a changing attack surface. Controlled testing across the full environment at regular intervals can show whether defenses are improving while reducing the operational risk of assessing live systems.