Rein Security raises $25 million Series A to secure AI agents at runtime
Rein Security raised a $25 million Series A co-led by Glilot Capital and Sienna Venture Capital, with Corner Ventures participating, bringing total funding to $35 million. Rein watches what AI agents do in production, holds each to its role and blocks harmful actions before they run. It reports 8x revenue growth since its January 2026 launch.
Rein Security announced its $25 million Series A on October 8. Glilot Capital and Sienna Venture Capital co-led the round, with participation from Corner Ventures, bringing total funding to $35 million. The company will put the money into product development, its "Agent Breakers" research and hiring.
Rein secures both applications and AI agents at runtime. It argues the biggest agent risks, such as hidden prompt injections, manipulated customer-facing agents and trust passed between agents, appear only while agents run and are missed by code scanning, posture dashboards and gateway logs. Rein sees each agent action, keeps agents to their assigned role and blocks harmful actions before they execute, without routing data through a gateway or proxy; it also offers supply chain security for agents.
The company says revenue has grown eightfold and its customer count fivefold since its January 2026 launch, and that it already secures thousands of agents across multiple industries. These figures are company-reported.