US and Israel-based Rein Security has raised USD 25 million in a Series A round co-led by Glilot Capital and Sienna Venture Capital.
The round also included participation from Corner Ventures, Atlacle, and RNP Capital Advisors, and brings Rein Security’s total funding to USD 35 million. Founded in 2024, the company develops a runtime security platform for enterprises, designed both to protect the AI agents organisations build and to defend against attacks carried out by AI-driven systems.
Rein plans to use the capital for product development, agentic research, and global hiring. Since launching in January 2026, Rein Security reports an eightfold increase in revenue and a fivefold increase in its customer base.
Runtime controls for agentic AI
The platform relies on patented sidecar technology that operates at runtime, at the point where agents execute actions. This gives security teams visibility into each line of code an agent runs and each resource it accesses, along with governance over agent activity and real-time guardrails that block harmful actions. The company also covers the agent supply chain and traces actions back to the code that triggered them. Company and customer data are not routed through a gateway or proxy.
The funding comes as enterprises extend AI agents’ access to business systems, data, and workflows. According to Gartner figures, the market for securing AI is projected to reach nearly USD 4.8 billion in 2027, a 68.7% increase from 2026, and nearly USD 7.7 billion by 2028. Rein Security argues that much of the risk sits in downstream actions agents take automatically, often on instructions passed from another system or agent rather than a person. Adversarial AI, which operates at machine speed, adds a second layer of exposure. The company is calling for a move away from posture and vulnerability management towards prevention and protection.
Matan Bar-Efrat, co-founder and CEO of Rein Security, said security has not kept pace with the autonomy of enterprise AI agents, and that the funding will support the infrastructure needed to deploy them with visibility and control.
Research findings and customer deployments
At Black Hat USA 2026, the company’s vulnerability research team, Agent Breakers, presented research showing how it compromised the AI shopping agent of a top-five retailer in the US. In a separate case, a global enterprise’s onboarding agent opened a PDF containing a hidden prompt injection that directed it to act outside its intended role. Rein Security detected and blocked the action.
According to the company, the platform secures thousands of AI agents executing millions of actions. Customers include Lemonade, whose services reach more than three million active customers, and Dun & Bradstreet, whose agentic products serve over 240,000 customers. New customers Flex and Swimlane extend the company’s presence across financial services, healthcare, SaaS, data, retail, and energy.
Investors framed the round around the gaps in existing frameworks. Arik Kleinstein of Glilot Capital described agent security as a fast-moving and underserved area. Thomas Visan of Sienna Venture Capital said current frameworks are not equipped for agents operating directly in production environments.
