Founding Full-Stack Engineer (AI, React.js, Next.js) - Relocation support to Berlin

Salary Transparency:

• The gross annual salary range is between €100,000 and €130,000 plus equity stake (founding stock options).
• This position is intended for candidates with over 5 years of professional experience.
• Location: Berlin (on-site). Relocation support provided, if needed.
• Three hires will be made for this position.

Muxon is a small, globally active recruiting agency managing this search on behalf of an early-stage, Berlin-based startup, recently backed by one of the world’s most important accelerators. We are recruiting three hands-on Founding Software Engineers to join a compact, 2-people founder-led team on-site in Berlin — a role that offers real ownership, significant equity, and the opportunity to shape product and architecture from day one.

Requirements:

• Early-startup or founding experience.
• Background in B2C software
• Experience developing visual effects software, animations, or similar.
• Minimum 5 years professional full-stack development experience.
• Proven experience with TypeScript, React.js, and Next.js.
• Experience with LLMs / generative AI.
• Experience with relational databases (preferably PostgreSQL) and cloud platforms (GCP or AWS).
• Strong product ownership, high velocity in ambiguous environments, and an entrepreneurial mindset.
• Professional English (C1) and willingness to work fully on-site in Berlin.

Responsibilities:

• Own end-to-end development of user-facing features across frontend and backend.
• Design and implement scalable architecture for growth to millions of users.
• Build and optimize systems integrating LLMs and agentic tool-calling where relevant.
• Drive technical decisions, run evaluation frameworks (automated benchmarks, A/B tests), and optimize inference performance and cost.
• Collaborate directly with founders on roadmap and product direction.

Benefits:

• Equity stake (founding stock options).
• Above-market salary and competitive package.
• Company-paid lunch & dinner.
• Relocation support to Berlin is provided, if needed.
• Work on a consumer AI product used by thousands daily with high founder impact.

If you’re driven to build a category-defining product and want real ownership from day one, apply — We are actively sourcing strong candidates for this founding role.