AI Startup Rein Security Raises $25M in Series A Funding

Rein Security, a NYC-based provider of an AI-native runtime security platform for enterprises, has raised $25 million in a Series A funding round, bringing the total amount 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.

The company plans to use the funding to accelerate product development, advance research into agentic AI security, and support global hiring.

What is Rein Security?

Rein Security develops a security platform designed to protect AI agents used by enterprises. As businesses increasingly rely on AI agents to access company systems, data, and workflows, these tools can create security risks that traditional solutions may not detect.

Read More:California-Based Gallatin AI Raises $50M in Series A Funding

Rein's platform uses patented sidecar technology to monitor AI agents while they operate. It tracks the code they execute, and the resources they access, giving security teams visibility into agent activity and allowing them to block harmful actions in real time.

The platform also helps secure the AI agent supply chain without routing company or customer data through a gateway or proxy.

How Much Funding Has Rein Security Raised?

Rein Security has raised $35 million in total funding following its latest $25 million Series A round.

The company has not disclosed the amount or date of its previous funding round in the announcement.

Who Invested in Rein Security’s Series A?

The $25 million Series A round was co-led by:

• Glilot Capital
• Sienna Venture Capital

Other participating investors include:

• Corner Ventures
• Atlacle
• RNP Capital Advisors

Why the Funding Matters

Rein Security plans to use the new funding to accelerate product innovation, advance its research into agentic AI security, and expand its global team.

The investment comes as enterprises deploy AI agents across business systems, and workflows. Rein aims to strengthen its ability to monitor agent activity, identify vulnerabilities and prevent harmful actions as AI adoption grows.

Who founded Rein Security?

Rein Security was founded in 2024 by Netanel Rubin and Matan Bar-Efrat.

The company is headquartered in New York City, and focuses on security solutions for enterprise AI agents.

"Enterprise AI agents are becoming essential to how businesses operate, but security hasn't kept pace with the autonomy these systems now have," said Matan Bar-Efrat, co-founder and CEO of Rein Security. "This funding enables us to keep building the infrastructure enterprises need to deploy AI agents with visibility, control and confidence."

"The agent economy is upon us, and the rapid adoption of AI agents is creating a fundamental shift in enterprise security," said Arik Kleinstein at Glilot Capital. "As agents gain the ability to access systems, make decisions and act autonomously, enterprises need a new approach built specifically for this new landscape.

Market and Business Growth

Rein Security's platform is already protecting thousands of AI agents that perform millions of actions, according to the company.

Its customers include Dun & Bradstreet and digital insurance company Lemonade. Rein protects AI agents supporting Lemonade's services for more than three million active customers. Its platform also supports agentic products used by over 240,000 Dun & Bradstreet customers.

At Black Hat USA 2026, Rein's vulnerability research team, Agent Breakers, presented research demonstrating how it compromised the AI shopping agent of a top-five US retailer.

What Happens Next?

Rein Security plans to accelerate product development, advance its agentic AI security research, and expand its global hiring.

The company will continue developing its runtime security platform to help enterprises monitor AI agents, control their actions, and respond to emerging threats as adoption increases.

Read More:California-Based Atomic Machines Secures $250M in Funding