Rein Security raises $25M to guard enterprise AI agents

Rein Security, a startup that protects the AI agents companies build, has raised a $25 million Series A, The AI Insider reported on October 9, 2026. Glilot Capital and Sienna Venture Capital co-led the round. AI agents are programs that take actions on their own, such as calling tools, moving data or making purchases. As companies hand them more work, watching what they actually do has become a security job of its own.

The round

The new money brings Rein's total funding to $35 million, according to both The AI Insider and CTech by Calcalist. The investors are:

Investor	Role
Glilot Capital	Co-lead
Sienna Venture Capital	Co-lead
Corner Ventures	Participant
Atlacle	Participant
RNP Capital Advisors	Participant

Rein says it will spend the money on product development, research into AI agents and hiring around the world. No valuation was disclosed.

What Rein does

Rein sells what it calls an AI-native runtime security platform. "Runtime" means it works while the agent is running, not only when its code is written. The product watches agents where they take actions and can stop them in real time.

It covers four areas, The AI Insider reports:

• Visibility into each agent's code and the resources it can reach
• Governance over what agents are allowed to do
• Real-time guardrails that block risky actions as they happen
• Agent supply chain security, checking the tools and parts agents are built from

The product relies on what Rein calls patented "sidecar" technology, a small helper that runs next to each agent. "We operate within the customer's cloud environment using a completely different technology," co-founder Netanel Rubin told Calcalist. Rein says company and customer data never has to pass through a gateway or proxy.

Growth and customers

Rein launched its product in January 2026. Since then, revenue has grown eightfold and the customer base fivefold, according to both reports. The company says it secures thousands of agents that carry out millions of actions.

Named customers include Dun & Bradstreet, Lemonade, Flex and Swimlane, The AI Insider reports. "Rein helps us see and control what our agents do at scale," said Jay DePaul, chief cybersecurity and technology risk officer at Dun & Bradstreet.

Rein's research team, called Agent Breakers, is also presenting at Black Hat USA 2026. In its research, the team compromised the AI shopping agent of an unnamed top-five U.S. retailer.

The company

Rein was founded in 2024 and is based in New York and Tel Aviv. Matan Bar-Efrat is co-founder and chief executive, and Netanel Rubin is co-founder. It has 31 employees, Calcalist reports.

"Security hasn't kept pace with the autonomy these systems now have," Bar-Efrat said. Arik Kleinstein of Glilot Capital said "enterprises need a new approach built specifically for this new landscape."

The round lands in a busy week for AI security funding. Hadrian raised $40 million for AI agents that test a company's defenses.

What this means for developers

• List the agents you already run. Rein's pitch starts with visibility. Before buying any tool, know which agents run in your company, what they can reach and who owns them.
• Limit what each agent can touch. The cheapest guardrail is a narrow set of permissions. Give agents only the tools and data a task needs.
• Check the parts agents are built from. Agent supply chain risk is real: a bad tool or plugin can act with the agent's access. Review third-party tools the way you review dependencies.
• Ask vendors where data flows. Rein says its sidecar avoids routing data through a gateway. For any agent security product, confirm whether your data leaves your cloud.
• Watch the Black Hat research. Attacks on shopping agents show what can go wrong when agents can spend money. Test your own agents against similar tricks.

Expect more funding rounds like this one as companies move agents from pilots into production.