Rein Security Raises $25M for AI Agent Runtime Security

Rein Security has raised $25 million in Series A funding to protect enterprises from the new class of risks created by autonomous software, bringing the company's total announced capital to $35 million. The round, announced on October 8, 2026, was co-led by Glilot Capital and Sienna Venture Capital, with participation from Corner Ventures, Atlacle, and RNP Capital Advisors. The financing puts a spotlight on AI agent runtime security, a fast-emerging discipline focused on controlling what AI agents actually do once they are running inside corporate systems.

Founded in 2024 and co-headquartered in New York and Tel Aviv, Rein is betting that checking an agent's permissions before deployment is no longer enough. According to the company, its platform uses patented sidecar technology positioned inside the customer's cloud environment, observing agents as they execute code and interact with business systems in real time. The approach is designed to spot dangerous behavior while actions are taking place, and to block harmful ones before they land. It is this live-monitoring pitch that defines the AI agent runtime security category.

Why AI agent runtime security is becoming a board-level concern

The timing of the round reflects how quickly enterprises are handing AI agents the keys to sensitive infrastructure, and why investors see AI agent runtime security as a category with real enterprise demand. According to industry reporting, agents can be manipulated through ordinary-looking documents, emails, websites, and other inputs, and an agent with legitimate access to sensitive systems may still be induced to take unauthorized actions by instructions embedded in retrieved content. Rein argues that legacy tools, built to scan static permissions or vulnerabilities, cannot see this exposure at all.

The company's pitch to security teams is visibility at the point of execution, which is the core promise of AI agent runtime security. Rein says its technology can monitor the resources agents access, trace activity back to the code that produced it, and enforce guardrails without forcing organizations to route their data through a centralized proxy. That last point matters to regulated buyers, who often refuse to pipe customer data through third-party gateways. Reported by Fintech Global, Gartner forecasts that spending on AI security will climb to nearly $4.8 billion in 2027, up 68.7 percent on 2026, before approaching $7.7 billion by 2028.

The threat is two-sided. Companies must protect the agents they develop themselves while also defending against attackers who are deploying AI of their own. Rein's research unit, known as the Agent Breakers team, has demonstrated both halves of the problem. The team presented research at Black Hat USA 2026 showing how a major U.S. retailer's shopping agent could be compromised, and the company separately reported uncovering a prompt injection hidden inside a PDF targeting a global enterprise, according to coverage by Calcalistech.

The founders and the bet investors are underwriting

Rein was founded by Matan Bar-Efrat and Netanel Rubin, two veterans of Israel's Unit 8200 intelligence corps. Bar-Efrat previously worked in European sales and business development at Cyberbit and Elbit Systems, while Rubin led vulnerability research at Check Point and founded the cybersecurity startup Holcy. The company employs 31 people, with offices in Tel Aviv and New York.

The founders did not begin with agent security. According to reporting by RuntimeWire, their first idea was cyber-insurance software that would use security data to help insurers price risk. When buyers proved slow to pay, the founders pivoted toward a problem with more immediate operational cost: teams could not reliably tell which vulnerabilities in running applications were actually reachable or dangerous. AI agent runtime security is the natural extension of that instinct, moving the check from what software looks like to what it is doing right now.

Investors are paying for evidence of enterprise appetite. Since its product launch in January 2026, Rein says revenue has grown eightfold and its customer base fivefold, with named customers including Dun & Bradstreet, Lemonade, Flex, and Swimlane. The company reports that it currently secures thousands of agents executing millions of actions. Those are company-reported metrics without independently audited baselines, so the honest reading is directional: enterprises are already budgeting specifically for agentic security. Dedicated AI agent runtime security budget lines are starting to appear in enterprise plans. The fresh capital will go toward product development, expanding agentic AI security research, and global hiring, Pulse2 reported.

What the Rein round says about the agent economy

Rein is part of a broader wave of funding aimed at the infrastructure layer beneath autonomous software, and AI agent runtime security is emerging as one of its sharpest battlegrounds. Just this month, TypeSafe AI raised $870 million for models designed to deliver structured decisions directly to software, while Meta and Sierra published a draft of the Personal Agent Protocol to standardize how agents interact with businesses. Security, payments, and protocols are being built in parallel, because an agent that can act in the world needs guardrails, a wallet, and a common language.

The open question for the sector is whether runtime controls can actually stop unauthorized actions in live workflows. Rein's core claim is that enforcement must happen alongside execution, not before it, and that internal agents built by the enterprise itself deserve as much scrutiny as third-party tools. Buyers should test that claim against their own agent permissions and workflows; investors should keep asking for the absolute revenue and customer figures behind the growth multiples. If the answer holds up, AI agent runtime security may become one of the more durable categories in the agent economy. It is rare that a $25 million check gets written to a question that big in a company with 31 people, which is precisely why this round is worth watching.