Rein Security Lands $25M Series A to Secure AI Agents

Rein Security, an AI-native runtime security startup, announced on October 8, 2026 that it has closed a $25 million Series A funding round to secure enterprise AI agents where they actually do their work: in production. The round was co-led by Glilot Capital and Sienna Venture Capital, with participation from Corner Ventures, Atlacle and RNP Capital Advisors, according to SecurityWeek. The new financing brings Rein Security's total funding to $35 million.

Founded in 2024 and co-headquartered in New York City and Tel Aviv, Rein Security began as an application-runtime protection company before turning its technology toward the agent economy. The thesis, according to Pulse 2.0, is that AI agents present a security problem traditional tools were never designed for: software that perceives, decides and acts inside live business systems without a human directing every step.

Why runtime matters for agentic AI

The central pitch of Rein Security is timing. Most security tooling inspects code before it ships or scans infrastructure for known vulnerabilities. Agents break that model because the risky moment is execution itself: an agent may follow a rule it learned in training, chain together legitimate permissions, and carry out an action that no scanner would ever flag as anomalous. According to Pulse 2.0, the risks can emerge from downstream actions initiated automatically by AI agents, including actions triggered by instructions originating from other applications or agents rather than directly from a person.

The backdrop is a rapidly escalating threat landscape. Tech Startups has reported on cases where criminals and state-linked groups used AI models across portions of attack chains, including reconnaissance and work related to zero-day vulnerabilities. In the same week Rein Security announced its round, rival Hadrian raised $40 million for AI-driven offensive security, reported by Tech Startups — evidence that investors now treat agentic AI security as a standalone category rather than a feature inside existing suites.

Enterprises face a two-sided problem, as the Rein Security founders describe it. On one side sit the AI agents companies build and deploy themselves, which receive broad permissions to touch business applications, data and workflows. On the other side sit AI-powered attacks that probe those same systems. Rein Security aims to address both sides at once, according to CTech, which interviewed co-founder Netanel Rubin.

Sidecar technology that watches agents in action

Rein Security's answer is what it calls patented sidecar technology: security controls that run alongside AI agents at runtime, in the customer's own environment, observing what the agents do as they do it. The platform gives security teams visibility into the code agents execute and the resources they access, along with governance controls and real-time guardrails intended to block potentially harmful activity before it completes, according to SecurityWeek.

That architecture reflects a deliberate design choice. Rein Security's platform operates within the customer's cloud environment rather than routing company or customer data through a gateway or proxy, reported by CTech. The distinction matters for adoption: security teams increasingly resist tools that would duplicate sensitive data flows, and in-agent observation avoids that cost while keeping enforcement close to the action.

Rein Security also applies the approach across the AI agent supply chain, protecting agents built internally by the enterprise as well as defending against AI-powered attacks directed at agent systems. In a conversation with CTech, co-founder Rubin said that while much industry attention goes to securing agents developed outside an organization, Rein Security focuses on the agents companies build for themselves — a segment where shadow deployments on individual machines complicate governance.

The founders bring relevant pedigrees to the problem. Matan Bar-Efrat and Netanel Rubin both served in Israel's Unit 8200; Bar-Efrat later worked in European sales and business development at Cyberbit and Elbit Systems, while Rubin led vulnerability research at Check Point, according to RuntimeWire. The company employs 31 people across its Tel Aviv and New York offices.

Investors bet on early traction

Glilot Capital's Arik Kleinstein framed the round around the scale of the shift underway, saying in the announcement that the agent economy has arrived and that rapid AI agent adoption is creating a fundamental change in enterprise security, with autonomous agents requiring security built for their specific landscape, according to SecurityWeek.

The startup says its solution already secures thousands of agents across multiple industries. Since its January 2026 commercial launch, Rein Security reports that revenue grew eightfold and its customer base grew fivefold, with customers including Flex, Swimlane, Lemonade and Dun & Bradstreet, according to reporting by The Jo AI.

The fresh capital will fund three priorities: accelerating product development, expanding the company's agentic AI security research, and growing its global team, according to Pulse 2.0. For Rein Security, the bet is that as enterprises hand agents more autonomy, the layer that watches what agents do at runtime becomes as essential as the agents themselves — and that the winners in agentic security will be the platforms that prove it with evidence, not alerts.