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.
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