Arceus, a San Francisco-based law firm launched in 2026, announced a $17 million fundraise led by Greycroft on October 1, 2026. The firm combines licensed attorneys with AI agents and proprietary software to provide commercial legal services, including contract review, drafting and negotiation, for a flat fee. Its clients often include startups and scale-ups. Arceus guarantees standard reviews within eight hours or the review is free.

Arceus built CounselOS, a proprietary operating system that gives its attorneys context about a company’s business, preferences, agreements, prior decisions and negotiation history. It connects to platforms including HubSpot, Salesforce, Gmail and Slack to gather that information, identify issues and route matters to the appropriate attorney. Founder and CEO Mac Liu said he started the firm after experiencing missed deadlines, repeated back-and-forth and unexpectedly high bills at other firms. He criticized the billable-hour model, saying it incentivizes firms to take longer, and said Arceus aims to provide speed, responsiveness, transparency and service.

Greycroft partner Mark Terbeek said many legal AI companies sell software to existing firms, while he sees Arceus as rebuilding the law firm itself. The article describes Arceus’s structure—combining an MSO, flat fees, faster work, AI and lawyers—as increasingly common among new model law firms in the US, UK and Europe over roughly nine months. It says Arceus stands out among peers for raising $17 million so early. The article also lists Legal Innovators UK on November 4 and 5 and Legal Innovators New York on November 17 and 18, with complimentary tickets for qualifying law firm or in-house legal team attendees.

Arceus, a San Francisco-based law firm launched in 2026, announced a $17 million fundraise led by Greycroft on October 1, 2026. The firm combines licensed attorneys with AI agents and proprietary software to provide commercial legal services, including contract review, drafting and negotiation, for a flat fee. Its clients often include startups and scale-ups. Arceus guarantees standard reviews within eight hours or the review is free.

Arceus built CounselOS, a proprietary operating system that gives its attorneys context about a company’s business, preferences, agreements, prior decisions and negotiation history. It connects to platforms including HubSpot, Salesforce, Gmail and Slack to gather that information, identify issues and route matters to the appropriate attorney. Founder and CEO Mac Liu said he started the firm after experiencing missed deadlines, repeated back-and-forth and unexpectedly high bills at other firms. He criticized the billable-hour model, saying it incentivizes firms to take longer, and said Arceus aims to provide speed, responsiveness, transparency and service.

Greycroft partner Mark Terbeek said many legal AI companies sell software to existing firms, while he sees Arceus as rebuilding the law firm itself. The article describes Arceus’s structure—combining an MSO, flat fees, faster work, AI and lawyers—as increasingly common among new model law firms in the US, UK and Europe over roughly nine months. It says Arceus stands out among peers for raising $17 million so early. The article also lists Legal Innovators UK on November 4 and 5 and Legal Innovators New York on November 17 and 18, with complimentary tickets for qualifying law firm or in-house legal team attendees.