Harvey has announced a $550m funding round at a $15.5B valuation, co-led by Diffusion and Lightspeed Venture Partners. It has also bought San Francisco-based Guardrails AI, an AI security platform for agents.

Guardrails is a pioneer of AI reliability and simulation infrastructure, they said. They created the first open-source AI guardrails that help teams find where their agents stray from intended behaviour and manage agent risk in real time. Guardrails’ co-founders, Shreya Rajpal and Zayd Simjee, and their team will join Harvey’s product and engineering organization. This marks Harvey’s fourth acquisition of 2026.

The latest raise follows the introduction of Harvey’s first post-trained open-weight model and the launch of Harvey LAB, the Legal Agent Benchmark. It will accelerate Harvey’s efforts to help law firms, in-house legal teams, and professional services firms build and own their intelligence at scale, they said.

Existing investors Sequoia, Kleiner Perkins, a16z, Coatue, Conviction, Elad Gil, Evantic, GIC, Goldman Sachs Alternatives, Verified Capital, and WNDR participated in the round. New investors include Diffusion, Lightspeed, Sapphire Ventures, and Whale Rock.…

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