San Francisco based Harmonic Security closes £37.7m series B
This article covers Harmonic Security, a London- and San Francisco-based AI security startup, which has closed a series B funding round of £37.7m. The funding will be used to expand engineering and go-to-market teams in the US and UK and to help enterprises and security teams monitor and control employee AI use.
Harmonic Security has closed a series B funding round of £37.7m, taking its total financing to £57.4m. The London- and San Francisco-based company, which builds tools to monitor and control workforce AI use, says the capital will be used to expand engineering and go-to-market teams across the US and the UK. The raise matters because businesses are increasingly wrestling with how to manage employee AI use without blocking productivity.
Why it matters
Enterprises are adopting generative AI and desktop assistants quickly, but governance and data risk remain major blockers. Harmonic positions itself in that gap: it aims to give security and business teams visibility into who is using AI, how they are using it, and which interactions create value. For organisations weighing whether to restrict tools or enable them safely, the outcome affects productivity, compliance and potential exposure of sensitive data.
Inside the product
Harmonic’s platform classifies AI tasks, surfaces why they are used, and enforces controls in real time. The company says it has extended coverage beyond browser-based monitoring to desktop tools and agentic workflows, bringing those data sources into a single platform so security teams can spot where risky behaviours typically begin, such as personal-account use or credential leakage.
A core technical differentiator Harmonic highlights is its use of small language models to interpret each AI interaction in context and at speed. That contextual analysis powers a Usage Intelligence layer that reports which AI use cases are delivering value, which teams have adopted faster workflows, and where to invest rather than clamp down.
Harmonic reports protecting AI use for millions of employees at more than 100 organisations and has signed distribution partnerships with Climb and Distology. It also lists integrations with Cisco Cloud Control’s Agent Builder via Model Context Protocol and with Claude’s Compliance API, which connects to Anthropic-hosted enterprise deployments. The company has grown to over 90 people across the United States and the United Kingdom and plans to use the new capital to hire across engineering and sales.
Who are the investors?
The round was described as oversubscribed and increases Harmonic’s total funding to £57.4m. Existing investors participated alongside new capital.
Zach Sivertson, Managing Director, Crosspoint Capital Partners, said:
Security has too often slowed the adoption of new technology. As organizations embrace AI, they shouldn’t have to choose between moving quickly and maintaining control. Harmonic gives leaders the visibility and confidence to accelerate adoption, while empowering employees to use the tools that make them more productive, all with the right guardrails in place. We’re proud to partner with Alastair and the Harmonic team.
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Founder perspective
Alastair Paterson, CEO and Co-Founder of Harmonic Security, framed the company’s work around two questions boards are asking about AI: reducing risk and proving value. He said:
Every board I talk to is asking two questions: how do we reduce the risk of AI use, and are we getting value? Most vendors struggle to answer the first, yet we address both. From the very start, we doubled-down on our custom small language models, which means we can benefit from a unique insight into enterprise AI use.
On the fundraising and next steps, Paterson added:
We've got some real momentum, and I know we’re just getting started. This round means we get to build that out faster and continue rapidly responding to the AI landscape shifts. These remarks underline a product-first pitch focused on contextual analysis rather than simple pattern matching, and a commercial push into enterprise accounts on both sides of the Atlantic.
The bigger picture
The raise comes as demand for tools that combine AI governance with productivity insight is rising. The funding also signals continued appetite from AI investors for companies tackling enterprise risk and observability, especially those that can integrate with large vendor ecosystems such as Cisco and Anthropic.
For the UK and European ecosystem, the deal highlights a pattern: homegrown AI security companies are attracting transatlantic capital and aiming to scale engineering and sales footprints across markets. As regulation and compliance scrutiny grow in Europe, tools that deliver context-aware controls and demonstrable value will be central to how organisations adopt generative AI safely.
They've invested in Harmonic Security
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