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Israeli startup Rein Security raised a $25M Series A co-led by Glilot Capital and Sienna Venture Capital, and says revenue is up eightfold since January 2026.
Key Takeaways
- Rein Security raised a $25M Series A, co-led by Glilot Capital and Sienna Venture Capital, on October 9, 2026.
- The company reports 8x revenue and 5x customer growth since its January 2026 product launch.
- Total funding now stands at $35M. Valuation was not disclosed.
Lead
Rein Security, a Tel Aviv and New York cybersecurity startup, announced a $25M Series A on October 9, 2026. The round was co-led by Glilot Capital and Sienna Venture Capital, with Corner Ventures, Atlacle and RNP Capital Advisors also participating. The company puts its total funding at $35M and did not disclose a valuation.
Rein says revenue has grown eightfold and its customer base fivefold since it launched its product in January 2026. Those figures are company-reported and unaudited, and Rein gave no absolute revenue or customer numbers.
What Does Rein Security Actually Sell?
Rein sells runtime security for AI agents: software that watches what an agent does while it executes, rather than screening traffic at the network edge. Its patented "sidecar" technology runs inside the agent's execution environment. The company says that gives security teams visibility into every line of code an agent runs and every resource it touches.
On top of that visibility, the platform applies governance rules and real-time guardrails that can block a harmful action before it completes. Rein says this works without routing sensitive data through an external gateway or proxy. That claim separates it from gateway-style products, which inspect traffic at a chokepoint.
The company says it now secures thousands of agents executing millions of actions. Named customers include Lemonade, Flex, Swimlane and Dun & Bradstreet.
Why Are Investors Paying for Agent Security Now?
Enterprises are giving AI agents access to business systems, data and workflows faster than security teams can map what those agents do. Traditional tools were built to watch people and static applications, not software that decides its own next step. That gap is the opening Rein and its competitors are selling into.
The company frames the problem in two parts. Agents built informally by employees on their own machines are one exposure, and agents built by the organization itself are another. At Black Hat USA 2026, Rein demonstrated a vulnerability in the AI shopping agent of a top-five U.S. retailer. The company also says its platform detected and blocked a prompt injection attack hidden inside a PDF.
Market forecasts point the same direction. Gartner projects the AI security segment will reach $4.8B in 2027, a 68.7% rise, and $7.7B by 2028.
How Does This Round Compare With the Last One?
The Series A is roughly three times the size of the company's seed. Rein emerged from stealth in January 2026 with an $8M seed led by Glilot Capital, backed by security founders from Aqua Security and Talon. Glilot returning as co-lead of the follow-on is the plainest signal in the round, since the investor with the most information chose to increase its exposure.
The arithmetic is worth a note. An $8M seed plus a $25M Series A comes to $33M, while the company cites $35M in total funding. The gap is not explained in the announcement.
The growth claims deserve the usual caution. An eightfold rise in revenue from a launch-month base can mean a small starting number. Without disclosed revenue, the multiple shows momentum but not scale.
Who Competes in This Segment?
Rein is entering a crowded field of agent security vendors. Zenity, Obsidian Security, Eve Security and Armadin work on adjacent problems, and Zscaler has moved into the area through its broader platform. Most compete on governance and discovery of agents. Rein's argument is that execution-level visibility catches behavior that perimeter and gateway tools cannot.
That argument is untested at large scale. Gateway products are easier to deploy because they sit outside the application, while a sidecar must run alongside each agent. Whether enterprises accept that deployment cost will shape how far Rein can expand beyond early adopters.
Founders and Use of Funds
Rein was founded in 2024 by CEO Matan Bar-Efrat and CTO Netanel Rubin, both Unit 8200 alumni. The company employs 31 people. It plans to use the new capital to accelerate product development and expand its research efforts.
Outlook
Rein now has $25M, a returning lead investor and a customer list with recognizable names, all within about nine months of launch. The open questions are the revenue base behind the eightfold figure and whether runtime sidecars can win against gateway tools in large enterprise deployments. With Gartner forecasting rapid growth in AI security spending through 2028, competition for those budgets will intensify, and Rein's next disclosures on customers and revenue will show how much of its early momentum holds.
