Rein Security, an AI-native platform protecting enterprises at runtime, has secured $25m in a Series A round as companies race to hand autonomous AI agents deeper access to their systems before the tools to police them have caught up.
Glilot Capital and Sienna Venture Capital jointly led the investment, with Corner Ventures, Atlacle and RNP Capital Advisors also taking part. The raise lifts the firm’s total capital to $35m.
The deal arrives as businesses grant AI agents wide reach into corporate data, applications and workflows, opening up threats that legacy security tools cannot spot or halt. Gartner forecasts that spending on AI security will climb to almost $4.8bn in 2027, a 68.7% increase on 2026, before reaching close to $7.7bn by 2028. Organisations now confront a twin problem: protecting the agents they develop while also fending off attackers who wield AI themselves.
Much of this exposure is new and difficult to see. It emerges from the automated downstream steps agents perform across business systems, frequently triggered by instructions from another machine or agent instead of a human. Adversarial AI compounds the pressure by striking at machine speed. Rein argues this demands a move away from posture and vulnerability management towards prevention and protection.
The company’s platform runs on patented sidecar technology positioned where agents actually carry out actions. Security teams gain sight of each line of code an agent executes and each resource it reaches, plus governance controls and live guardrails that stop damaging behaviour. Rein also protects the agent supply chain without passing company or customer data through a gateway or proxy.
Evidence of these threats is already surfacing. At Black Hat USA 2026, Rein’s research unit, Agent Breakers, demonstrated how it took control of an AI shopping agent belonging to one of the five largest US retailers. In a separate case, a global enterprise’s onboarding agent opened a seemingly harmless PDF containing a concealed prompt injection that pushed the agent beyond its assigned role. Rein identified and stopped the action before harm occurred.
Rein plans to direct the fresh capital towards product development, agentic research and international recruitment. Since launching in January 2026, the firm has multiplied revenue eightfold and its customer count fivefold. Recent clients such as Flex and Swimlane extend its presence into financial services, healthcare, SaaS, data, retail and energy. The platform now protects thousands of agents performing millions of actions, including for Dun & Bradstreet, whose agentic products serve more than 240,000 customers, and InsurTech firm Lemonade, which has over three million active customers.
Rein Security co-founder and CEO Matan Bar-Efrat said, “Enterprise AI agents are becoming essential to how businesses operate, but security hasn’t kept pace with the autonomy these systems now have. This funding enables us to keep building the infrastructure enterprises need to deploy AI agents with visibility, control and confidence.”
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