AI Security Firm HiddenLayer Raises $100M Series B

As coding agents take over writing and shipping code without a human in the loop, the points attackers can target are spreading fast beyond foundation models to autonomous agents themselves. Traditional security tools were built to protect code and infrastructure, not models that can be manipulated or poisoned through their own inputs.

HiddenLayer secures agentic, generative, and predictive AI applications across their entire lifecycle, from discovery and AI supply chain security to attack simulation and runtime protection.

The new funding will deepen its Agentic Runtime Security capabilities and grow a new product, Agent Harness Security. A real example HiddenLayer published makes clear what problem it solves: coding agents pull context from repositories, documentation, tools and MCP servers, which means a malicious instruction hidden anywhere in that context can get followed automatically. In one case, an instruction disguised as a “required license header” tricked a coding agent into copying that same payload into every repository it touched — a self-propagating attack. Agent Harness Security plugs directly into a coding agent’s runtime to detect and block that kind of prompt injection, secret exposure, and unsafe command execution as it happens, giving security teams a full trail from the prompt that started a task through the files opened, commands run, dependencies installed, code changed, and pull requests created.

HiddenLayer was founded in 2022 in Austin, Texas by Chris Sestito, Tanner Burns, and James Ballard. Sestito previously led threat research at security firm Cylance, where he witnessed attackers fool the company’s own Windows executable-classification AI model with an inference attack — an experience that led directly to founding HiddenLayer.

HiddenLayer announced a $100 million Series B led by Delta-v Capital, with participation from Ten Eleven Ventures, Morgan Stanley, M12 (Microsoft’s Venture Fund), and Booz Allen Ventures. The company previously raised a $6 million seed round in 2022 and a $50 million Series A in 2023 led by M12 and Moore Strategic Ventures, bringing total funding to $156 million.

Annual recurring revenue grew more than 10x over the past year, and the company signed more than 50 new platform customers spanning securities brokerage, banking, insurance, accounting, government, technology, IT services, pharmaceuticals, airlines, and the US defense and intelligence communities, plus international customers including a major pharmaceutical company and premium automotive and food and beverage brands. HiddenLayer also supports a leading frontier model provider in securing more than 700 million weekly users.

HiddenLayer’s researchers hold 39 granted patents and 65 pending, and developed the first comprehensive Adversarial Prompt Engineering (APE) Taxonomy. The team also contributes to CISA/JCDC, MITRE, NIST, OWASP, and OpenSSF, shaping red-teaming methodology and global AI governance discussions.

“We set out to pioneer trusted, secure use of AI for enterprises, long before most organizations saw the urgency we do today,” said Sestito. “This funding lets us keep growing the purpose-built team and platform required to meet that moment as agentic AI becomes core to how enterprises operate.” Delta-v Capital partner Dan Williams said traditional security tools weren’t built for models that can be poisoned, hijacked, or manipulated through their own inputs, and credited HiddenLayer with turning deep adversarial-AI research into a product CISOs actually rely on.

HiddenLayer is also strengthening its leadership team, recently naming Mike Gesnaldo as Chief Revenue Officer, and plans to deepen channel partnerships and expand internationally, starting with Europe and the wider EMEA region.

Acquisitions and mega-rounds are both piling into AI security

Large security vendors are buying up AI security startups wholesale. Switzerland’s Lakera agreed to be acquired by Check Point, and Protect AI was acquired by Palo Alto Networks for an estimated $700 million. Non-human identity security firm Astrix Security is also being folded into Cisco for $400 million, winding down standalone sales as it does. HiddenLayer, by contrast, remains independent as it closes this round.

Capital is also flowing into fresh rounds. Israeli-American Alice (formerly ActiveFence) raised $140 million with Samsung Electronics among its backers, and autonomous pentesting platform Horizon3 raised a $250 million Series E that pushed its valuation past $2 billion. The closest match to HiddenLayer’s new product is Neo, which installs sensors on employee endpoints to watch and control what AI agents actually do in real time and raised a $100 million Series A. US-based AI security operations center TENEX.AI raised $250 million this April, crossing a $1 billion valuation.