Founding Product Engineer

Arceus is building a generational legal AI company, and we're looking for a Founding Product Engineer to build the core product from the ground up. You'll work shoulder-to-shoulder with attorneys and AI engineers to ship software that transforms how legal work gets done—something nobody has built before. This is your chance to set the engineering culture and standards for everyone who comes after you, while owning features that real customers depend on every day. We’re a high-ownership, fast-paced team that works 6 days a week and puts in long hours. It’s an intense environment, but one where you’ll have significant opportunities to take ownership, grow quickly, and make a meaningful impact.

What youll do

• Build and own core product features across the full stack, from data models to the interfaces attorneys and clients use daily.
• Partner closely with AI engineers and attorneys to turn legal workflows and review playbooks into reliable, production-grade software.
• Make pragmatic architecture and tooling decisions that let us move fast now without compromising our future.
• Write maintainable code, build for reliability, and take complete ownership of what you ship in production.
• Help define engineering culture, standards, and hiring practices as the team grows.
• Move work over the finish line when it matters—customer experience always comes first.
• Sit next to your teammates, turning real legal judgment into software that ships fast and holds a high bar.

What Arceus is looking for

• 1–3 years building and shipping production software, ideally at an early-stage company or as a founder.
• Strong full-stack ability: TypeScript/React on the front end, a modern backend stack, and relational databases.
• Hands-on experience building with AI/LLMs, either professionally or in your own projects.
• A track record of owning features end-to-end and making sound engineering trade-offs under pressure.
• Comfort with ambiguity and a proven ability to thrive in fast-moving, high-ownership environments.
• Excellent judgment, communication skills, and a high bar for your own work.
• Product instincts and an entrepreneurial mindset—you think like an owner and move with urgency.
• Resilience and persistence: you find another way when things don't work, and you take pride in going above and beyond.

This is an in-person, full-time role based in San Francisco.