10 cybersecurity startups defending against AI-powered threats

Security is becoming a continuous job

Horizon3, Armadin and XBOW run autonomous attacks against live systems to expose weaknesses that can actually be exploited. depthfirst works closer to developers, identifying vulnerabilities and proposing fixes in their software workflows. The common direction is continuous testing as systems change.

The financing is substantial. Armadin disclosed $189.9m across seed and Series A rounds; Dealroom records the two at $214m combined. XBOW announced $120m in March and a $35m extension in May. Together with depthfirst’s $40m and $80m announcements, those three companies disclosed $464.9m of financing this year. Horizon3 raised $250m in August at a valuation above $2bn, co-led by NightDragon and NEA. It is the largest of the ten by headcount, with 548 people.

Investment is accelerating, but one tag cannot describe the market

The broader Dealroom AI Security category recorded $2.15bn across 119 VC rounds in the first eight months of 2026. That already exceeds the $933m recorded for the whole of 2025. These are different-length periods, rather than a year-on-year growth comparison.

The category’s boundaries need care. Inferact, Sycamore Labs and Pramaana Labs account for $242m of the 2026 figure, although their recorded products concern inference infrastructure, enterprise agents and data analysis. Exein, Torq, Horizon3, Glow and Zenity are missing from the tag. The chart shows investment in the existing category; our company selection follows their security work. The ten watchlist companies alone raised $1.68bn in 2026 to mid-September, including the September rounds for Exein and HiddenLayer.

Hiring adds another view of momentum

XBOW has the fastest growth, from roughly 116 to 305 employees in a year. Horizon3 is the largest team at 548 people, up 58%. Zenity grew 70% to 264. Among the rest, Torq grew 30% to 468, Exein 25% to 81 and HiddenLayer 7% to 176. Armadin, depthfirst, Onyx and Glow have no one-year comparison in Dealroom yet.

That distinction matters: the fastest percentage increase does not imply the largest business. Hiring gives us another signal of expansion alongside financing, while customer adoption and security outcomes remain the harder tests of progress.

The attack surface reaches beyond code

Torq’s $140m Series D backs AI-driven security operations, including alert triage, investigation and response. Exein adds the physical world, putting AI-based detection and protection directly onto connected devices. Dealroom records a $270m round for Exein in September at a $1.7bn valuation, as reported by the Financial Times. The round closed after the January–August period in the funding chart above. Glow left stealth in July with $180m at a $1.2bn valuation, led by Sequoia, Cyberstarts, Greenoaks and Redpoint, and rebuilds endpoint protection around stopping risky software and AI agents before they run.

Onyx, HiddenLayer and Zenity address AI systems themselves. Onyx controls enterprise agents; HiddenLayer protects models and AI applications at runtime; Zenity secures the actions autonomous agents take. These approaches address different routes through which an AI system could be compromised or act beyond its intended permissions.

Three recent rounds show the investment in this part of the market. Onyx raised a $113m Series B in July, led by Bessemer Venture Partners, four months after a $40m seed round. Zenity announced $125m in August, followed by HiddenLayer’s $100m Series B on 2 September. That is $338m across three companies. HiddenLayer’s September round falls outside the January–August funding chart above.

The companies worth following will turn these capabilities into protection customers can measure: exploitable weaknesses found, effective fixes deployed and attacks contained. That is the thread connecting this watchlist.