The financing round was co-led by Glilot Capital and Sienna Venture Capital, with support from Corner Ventures, Atlacle, and RNP Capital Advisors. This injection of capital brings the company's total funding to $35 million. Since its launch in January 2026, the firm has seen an eightfold increase in revenue, signaling intense demand for specialized security as corporations integrate AI into critical workflows.

Rein’s technology utilizes a patented sidecar architecture that operates at runtime, monitoring every action an agent takes without routing data through external proxies. This allows security teams to enforce real-time guardrails and block unauthorized commands. The need for such tools has become acute; the company’s research arm recently demonstrated how easily an AI shopping agent could be compromised, and they successfully neutralized a prompt injection attack embedded in a PDF within a global enterprise environment.

With new clients including Flex and Swimlane joining existing users like Dun & Bradstreet and Lemonade, the company plans to utilize the funds to accelerate product innovation and global hiring. As AI-related security spending is projected to reach nearly $4.8 billion by 2027, Rein is positioning itself to define the standards for agentic oversight, moving focus away from passive vulnerability management toward active, preventative protection.