The company opened a Dublin office earlier this year with plans to hire 40 people.

Legal AI start-up Harvey has raised $550m at a $15.5bn valuation in a round co-led by Diffusion and Lightspeed Venture Partners.

The round marks an almost $5bn valuation growth for the start-up, coming less than six months after it announced a $200m raise at an $11bn valuation.

Other investors, including Sequoia, Kleiner Perkins, a16z, Coatue, Conviction, Elad Gil, Evantic, GIC, Goldman Sachs Alternatives, Verified Capital, Sapphire Ventures, Whale Rock and WNDR, participated in the latest round.

Alongside the raise, Harvey also announced its acquisition of San Francisco-based Guardrails AI, a security platform for AI agents. Guardrails’ co-founders Shreya Rajpal and Zayd Simjee and their team will join Harvey’s product and engineering organisation, the legal-tech company said in an announcement today (9 September).

“The opportunity for companies to accelerate their competitive advantage with AI has never been higher,” Harvey co-founders Winston Weinberg and Gabe Pereyra said in a statement.

“Harvey wants to be the global partner legal teams turn to for this work, and we plan to hire and develop the best team in the space to support our clients through the next wave of AI transformation.”

The San Francisco-based Harvey provides AI for legal and professional services. Similar to many domain-specific large language models, its platform leverages data tuned using legal, tax and business knowledge, utilising a multi-model approach powered by leading AI models.

The company’s platform is used by a majority of the world’s largest law firms and by in-house legal teams at five of the Fortune 10, it said.

The latest funding round comes just after Harvey unveiled its first post-trained open-weight model, Harvey Tenet. The model has a base built from Chinese AI start-up Moonshot’s Kimi K3 and is trained specifically for legal tasks.

Earlier this year, the company opened an office in Dublin with plans to hire more than 40 employees over the next two years. The office was initially announced in January with early hiring plans eyeing 20 roles in the first year.

Don’t miss out on the knowledge you need to succeed. Sign up for the Daily Brief, Silicon Republic’s digest of need-to-know sci-tech news.