Rein Security raises $25M Series A to monitor AI agents at runtime
In brief
- Rein Security announced a $25 million Series A on October 8, 2026.
- Glilot Capital and Sienna Venture Capital co-led; Rein puts total funding at $35 million.
- Revenue grew 8x and customers 5x since Rein's January 2026 launch, the company says.
- Gartner expects the AI security market to reach nearly $4.8 billion in 2027.
Who's backing Rein
Corner Ventures, Atlacle and RNP Capital Advisors also took part in the round, per the report. CEO Matan Bar-Efrat and CTO Netanel Rubin founded the company in 2024, and it operates out of New York and Tel Aviv with 31 employees.
The funding math doesn't quite add up.
Rein launched its product in January 2026 after an $8 million seed round. Add the $25 million Series A and you get $33 million (the report doesn't explain the other $2 million in the $35 million total). Since launch, Rein says revenue has grown 8x and its customer base 5x. Those are the company's figures, and they haven't been independently verified.
How the sidecar works
Rein describes its platform as built on patented "sidecar" technology that sits alongside AI agents as they execute. The idea is runtime visibility: security teams can see the code an agent runs and the resources it touches, and the company says the platform can block harmful actions in real time.
Rein says it covers two fronts. One is protecting the AI agents enterprises build internally; the other is defending against AI-driven threats. It also says it does all this without routing data to external parties.
According to the company, its platform secures thousands of AI agents carrying out millions of actions. Rein says its customers span financial services, healthcare and retail, and it names Dun & Bradstreet and Lemonade among them.
The market Rein is chasing
Gartner expects the AI security market to reach nearly $4.8 billion in 2027, a 68.7% increase from 2026. The research firm's projection climbs to almost $7.7 billion by 2028.
On Gartner's numbers, that's one of the faster-growing corners of enterprise security, and it's the category Rein's new capital is going after.
Frequently asked questions
What does Rein Security's platform do?
Rein says its platform runs patented sidecar technology alongside AI agents as they execute, showing security teams the code agents run and the resources they touch. The company says it can block harmful actions in real time without routing data to external parties.
Who led Rein Security's Series A?
Glilot Capital and Sienna Venture Capital co-led the $25 million round, with Corner Ventures, Atlacle and RNP Capital Advisors also taking part. Rein says the raise brings its total funding to $35 million.
