Horizon3 has raised $250M in a Series E round, tripling its valuation to $2B in the year since June 2025. NightDragon and NEA co-led the round, joined by seven new investors and five returning backers.
The company sells autonomous security testing built around AI agents that live inside customer networks, probe for weaknesses using attacker-style techniques and produce a report card on what they find. The pitch: fix the holes before real attackers, increasingly AI-assisted, exploit them.
Horizon3 was founded in 2019 on the belief that AI will drive attacks at a speed and scale that human-centric defenses cannot match. It now counts more than 7,000 customers across banking, healthcare and other sectors, including four Fortune 10 enterprises, with 120% year-over-year ARR growth.
Chief revenue officer Matt Hartley says the funds will go primarily to go-to-market expansion through MSP and telco partners, with continued heavy R&D investment to keep pace with AI-driven threats.
The raise is the latest sign of investor appetite for AI-native security platforms as enterprises shift from human-led testing to continuous, machine-speed assessment.
