HiddenLayer announced a $100 million Series B on September 2, 2026, led by Delta-v Capital. Ten Eleven Ventures, Morgan Stanley, M12 (Microsoft’s venture fund), and Booz Allen Ventures also participated. The Austin company said it will put the money into its enterprise platform, including Agentic Runtime Security and Agent Harness Security, a new module aimed at autonomous coding agents.

The pitch is that models and agents now write and ship code, and that conventional tools built for repositories and networks cannot see a poisoned prompt or a hijacked tool call. HiddenLayer said it already supports a leading frontier model provider that serves more than 700 million weekly users, and that its researchers hold 39 granted patents and 65 pending patents.

Runtime first, then coding agents

Agentic Runtime Security is meant to watch how agents behave in production, flag manipulation, tool misuse, and unauthorized actions, and stop them as they happen. Agent Harness Security extends that runtime module to the harnesses that let coding agents write, review, and ship software with less human oversight.

Chris Sestito, chief executive and co-founder, said the round lets the company grow the team and platform as agentic AI moves into core operations.

“We set out to pioneer trusted, secure use of AI for enterprises, long before most organizations saw the urgency we do today. 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.” Chris Sestito, CEO and co-founder, HiddenLayer

Dan Williams, a partner at Delta-v Capital, said traditional security was built for code and infrastructure, not for models that can be poisoned or steered through their own inputs. HiddenLayer also named Mike Gesnaldo as chief revenue officer and said it will push further into Europe and the wider EMEA region.

Decoded Take

AI security is crowding up with firewall metaphors. HiddenLayer’s sharper claim is runtime on the agent harness, not another scanner for weights. The 700 million weekly users line is a customer the company will not name, which is useful for a press release and useless for a buyer who needs a reference. M12 and Booz Allen in the same round is a hint at both cloud and government demand. Watch whether Agent Harness Security can sit in front of Claude Code, Cursor, and internal coding agents without becoming the tool developers turn off, and whether the EMEA expansion produces a named European bank or ministry, not just a second office.