Rein Security has secured $25 million in a Series A funding round, bringing its total capital raised to $35 million. The round was co-led by Glilot Capital and Sienna Venture Capital, with participation from Corner Ventures, Atlacle, and RNP Capital Advisors. While the funding total is significant, the more compelling story lies in the company’s reported growth metrics. Since its product launch in January 2026, Rein claims its revenue has grown eightfold and its customer base has increased fivefold. These figures are company-reported and have not been independently audited, yet they serve as a potent demand signal for the specific type of security enterprises are prioritizing as they move agents into production.
The market for securing AI is expanding rapidly, with Gartner projecting the sector to reach nearly $4.8 billion in 2027, up 68.7% from 2026, and nearly $7.7 billion by 2028. According to IDC, 95% of companies now have AI agents deployed in production. However, the rapid adoption of these systems has outpaced existing security frameworks. As Matan Bar-Efrat, co-founder and CEO of Rein Security, noted in the company announcement and the PR Newswire release: “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.” This funding is intended to accelerate product innovation and expand the company’s research efforts.
The governance gap that enterprises are currently facing is not found in high-level dashboards or perimeter gateway logs. Instead, it is biting at the moment an agent executes an action. Rein addresses this through patented sidecar technology that operates at runtime, directly within the agent’s execution environment. This approach provides visibility into every line of code an agent runs and every resource it touches, allowing for real-time guardrails that block harmful actions before they occur. This architecture differs from an agent firewall or traditional gateway products, which typically sit at the perimeter rather than inside the execution flow. By operating as a sidecar, Rein provides governance and agent supply chain security without routing sensitive company or customer data through an external proxy.
The practical risks of this runtime gap were highlighted by a recent incident involving a global enterprise’s onboarding agent. The agent opened what appeared to be a standard PDF, but the file contained a prompt injection designed to force the agent to act outside its intended role. Rein detected and blocked the malicious action before any damage could occur. Furthermore, the company’s research team, known as the Agent Breakers, demonstrated at Black Hat USA 2026 how they could compromise the AI shopping agent of a top-five U.S. retailer. These examples underscore the vulnerability of autonomous systems when they lack granular, runtime-level oversight.
The shift in enterprise security requirements is clear to investors. Arik Kleinstein of Glilot Capital, as noted in SecurityWeek, stated: “The agent economy is upon us, and the rapid adoption of AI agents is creating a fundamental shift in enterprise security. As agents gain the ability to access systems, make decisions and act autonomously, enterprises need a new approach built specifically for this new landscape. This is a fast-moving and underserved area of security, and Rein has the platform, vision and early traction to help define it.” Similarly, Thomas Visan of Sienna Venture Capital observed: “As an enterprise’s technology ecosystem grows and evolves to include more AI agents that have a direct impact in production environments, security becomes an even greater concern. The frameworks that exist today are simply not equipped to handle this transition.” This demand is reflected in Rein’s roster of named customers, which includes Lemonade (services used by over three million active customers), Flex, Swimlane, and Dun & Bradstreet (agentic products serving more than 240,000 customers). Jay DePaul, chief cybersecurity and technology risk officer, Dun & Bradstreet, stated: “Our customers rely on Dun & Bradstreet for trusted data, and that trust has to extend to every AI agent we put into production. Rein helps us see and control what our agents do at scale, so we can keep innovating with agentic AI while protecting the customers who depend on us.”
This development is part of a broader maturation of the AI ecosystem. The industry is currently navigating an agent consolidation play, where security and governance are increasingly recognized as the primary barriers to widespread agent deployment. Simultaneously, the agent commerce stack is forming, with infrastructure for agent-led transactions maturing alongside security tools. Furthermore, the recent $52.5 million Series B for Stuut signals that the agent revenue layer is arriving, indicating that the infrastructure supporting agentic business models is becoming a priority for both builders and investors.
While Rein’s growth figures are notable, it is important to maintain a grounded perspective. The company’s reported growth remains unverified, and the market for AI security is highly competitive and fast-moving. Additionally, it remains to be seen how effectively the sidecar model will scale as agent frameworks continue to evolve and change. Despite these variables, the $25 million round suggests that the runtime layer of the agent stack is no longer a theoretical concern. Enterprises are now allocating real budgets to secure the point of execution, signaling that the governance gap is a tangible problem that requires immediate, specialized solutions.