RunSybil, a startup built around an AI agent that hacks into a company's own software to find weaknesses before an attacker does, has raised $40 million in a round led by Khosla Ventures. The company did not disclose its valuation.
The round drew participation from S32, Anthropic's Anthology Fund, Menlo Ventures, Conviction and investor Elad Gil, along with angel backers including Nikesh Arora, Amit Agarwal and Jeff Dean, plus other founders and executives from OpenAI, Palo Alto Networks, Stripe and Google.
Its agent, called Sybil, runs continuous penetration tests against software that is already live, probing systems the way a human attacker would: exploring, chaining vulnerabilities together and testing authentication boundaries to reach sensitive data. That is different from tools that scan source code for known flaws before an application ships.
Companies have historically relied on a mix of outside penetration testers, bug bounty programs and internal red teams to find these gaps. RunSybil says its system can automate much of that work, testing applications continuously as new code is deployed rather than on a fixed schedule.
The company argues this kind of testing has not kept pace with how quickly procurement, finance, engineering and other functions are being rebuilt around AI agents. Security testing, by contrast, is often still a scheduled event run by a separate team on its own timeline, a mismatch RunSybil says is hardest to manage in regulated industries such as finance, insurance and health care.
Ari Herbert-Voss and Vlad Ionescu founded RunSybil in 2023. Herbert-Voss joined OpenAI as its first security research hire in 2019 after leaving a machine learning doctorate at Harvard University; Ionescu previously ran offensive security red teams at Meta.
"We check every box that needs to be checked—for auditors, regulators and compliance teams," Herbert-Voss said. The bigger shift, he said, is turning security testing into a permanent capability built into how a company operates, rather than a one-off project.
Vinod Khosla, an early investor in OpenAI, told Fortune that "what it takes to add security and penetration testing to the AI world is definitely frontier—RunSybil is on the edge." Few people understand the space as well as Herbert-Voss does today, he said, though he expects established security vendors such as Palo Alto Networks to eventually compete for it. "We invest in founders who tackle large, unsolved problems with technically ambitious solutions," he added.
Its customers include startups such as Cursor, Turbopuffer, Notion, Baseten and Thinking Machines Lab, the company says, along with several large financial institutions and Fortune 500 companies it declined to name.
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