Rein Security raises $25M Series A to guard AI agents that enterprises build in house

Glilot Capital and Sienna Venture Capital co-led the round, with Corner Ventures, Atlacle and RNP Capital Advisors participating. Rein has now raised $35M, following an $8M seed. Matan Bar-Efrat and Netanel Rubin founded it in 2024. It has 31 employees and offices in Tel Aviv and New York. No valuation or ARR figure was given. The company says revenue grew eightfold and its customer base fivefold since the product launched in January 2026. Rein's patented sidecar runs inside the customer's cloud while agents are working. It records the code an agent executes and the resources it touches, and blocks harmful actions without sending data through a proxy. At Black Hat USA 2026, its research team showed how it took over the shopping agent of a top-five US retailer. Agent security is a crowded field, with dozens of startups, many of them Israeli. Rein focuses on agents companies build themselves rather than third-party tools. For teams shipping internal agents, that is a sign buyers will expect runtime guardrails.