Rein Security and the New Runtime Layer for AI Agents

Rein Security is building a runtime security layer for enterprise AI agents, software that can call APIs, reach sensitive systems and take business actions without a person approving every move. Founded in 2024, the company is led by Matan Bar-Efrat, co-founder and CEO, and Netanel Rubin, co-founder and CTO, from co-headquarters in New York City and Tel Aviv.

Rein matters now because the security problem changes once an AI agent moves beyond generating an answer. The real risk begins when language becomes execution: a file is opened, a tool is called, a database is queried or an instruction crosses a permission boundary. Rein's platform is designed to observe that moment and apply controls while the action is happening.

The company has early commercial momentum, fresh capital and a market racing toward the same problem. Rein reports 8x revenue growth and 5x customer growth since its January 2026 launch, with named users including Flex, Swimlane, Lemonade and Dun & Bradstreet. Its October 2026 Series A gives the team $25M to expand product development, security research and global hiring.

About Rein Security

Rein Security grew out of a question Bar-Efrat and Rubin kept hearing in conversations with more than 100 CISOs: why does application security produce so much noise while offering so little certainty about what actually happened in production?

That question became more urgent as enterprises began connecting AI agents to internal tools and data. Traditional application-security products can inspect code, scan dependencies or watch traffic at the edge. Those views are useful, but an agent can choose different code paths and tools at runtime. A prompt that looks harmless can still trigger an action the business never intended.

Rein's current answer is a patented sidecar architecture that operates alongside the agent. The company says its platform traces executed code and accessed resources, connects activity to business outcomes and enforces real-time guardrails. Rein also says customer data stays inside the customer's environment instead of moving through an external gateway or proxy.

That is a precise product thesis. The security boundary should sit close enough to execution to see what the agent actually did, not merely what a model was asked to do.

Why Rein Security Matters Right Now

Enterprise AI agents are moving from demos into workflows that affect finance, customer service, software development, operations and internal data. The more authority those agents receive, the less useful it becomes to treat security as a filter placed only at the prompt.

Rein says its platform already protects thousands of agents executing millions of actions. The company also reports 8x revenue growth and 5x customer growth since launch. Those figures show direction, not absolute scale: Rein has not disclosed revenue, customer counts or contract values. Still, the named deployments show where the company is aiming. Flex and Swimlane joined a customer group that also includes Lemonade and Dun & Bradstreet across financial services, insurance, SaaS, data, retail and energy.

The broader market is forming quickly. Gartner forecasts spending on securing AI will approach $4.8B in 2027 and $7.7B in 2028. That money will not flow into one neat category. Agent gateways, identity controls, governance platforms, data-security products and established AppSec vendors will all compete to define the control plane.

Leadership Built Around Product and Market Reality

Bar-Efrat and Rubin bring complementary operating histories to Rein. The company's official profile describes Bar-Efrat as a 14-year cybersecurity operator who worked in Unit 8200, scaled security products and advised companies on growth. Rubin began as a teenage pentester, served in Israel's Intelligence Corps and is now a second-time founder.

Their public founding story is grounded in field research rather than category theater. Rein says the founders spoke with more than 100 CISOs before launching. The recurring complaint was not a lack of alerts. It was the inability to determine which application risks were real, reachable and active in production.

That experience also explains Rein's dual identity. The company began by applying runtime context to application security, including API and software-composition risks. Its current positioning puts enterprise-agent security at the center. A January founder article described an architecture without sidecars, while the October Series A materials describe a patented sidecar. The public sources do not explain whether this reflects a new product layer, an architectural change or updated language, so buyers should evaluate the current design on its present merits.

Traction Meets a Crowded Security Market

Rein's strongest proof is not that agent security will matter. Almost every serious enterprise-security vendor now agrees with that premise. The harder question is where control belongs and which architecture can earn a permanent place in production.

An independent Omdia assessment described Rein's runtime context as differentiated while warning that the AppSec market is crowded and full of overlapping labels. Omdia's 2026 snapshot listed 24 employees and a direct-sales model serving large and midmarket enterprises across North America and EMEA. The report's advice was simple: Rein must make the product's place in the security stack unmistakable.

The $25M Series A gives Rein time and resources to make that case. Glilot Capital and Sienna Venture Capital co-led the round, with Corner Ventures, Atlacle and RNP Capital Advisors participating. Rein says total funding is $35M, although its publicly disclosed $8M seed and $25M Series A account for $33M. The reviewed announcements do not explain the remaining $2M.

Why Hiring Momentum Matters

Rein's official About page says the company is actively recruiting engineering and go-to-market talent. That combination is a useful market signal. Engineering hiring suggests the product and research surface is widening as new agent frameworks, tool protocols and attack techniques emerge. Go-to-market hiring suggests Rein believes enterprise demand is moving beyond experiments and into repeatable buying processes.

Hiring does not prove category leadership. It shows what the company must build next: deeper controls, clearer deployment paths, more threat research and a commercial system capable of explaining a new security layer to buyers who already own a crowded stack.

For operators considering Rein, the questions are practical. Can the platform see enough context to explain an agent's action? Can it block harmful behavior without slowing production? Can it integrate with existing identity, governance and application-security controls? Can the company turn early named users into durable, measurable adoption?

The Bigger Industry Shift

AI agents are forcing enterprises to redraw the line between software behavior and security policy. When an agent can decide which tool to call and which resource to access, the application is no longer following a fully predictable script. The security system must understand execution as it unfolds.

Rein Security is betting that runtime context becomes the record of truth for that world. The company has credible founders, public enterprise users, fresh funding and an urgent problem. Its next test is to prove that the point where language becomes action is not merely another feature in the security stack, but a control layer enterprises will refuse to operate without.