Staff Software Engineer - AI Features (Madrid)

About the role

Factorial is looking for a Staff Software Engineer in Madrid to build AI-native features into its product. It is a product engineering role: you write Rails and React, design systems and ship features with Product and Design, using LLM APIs the same way you use any other API. The team is office-first, with several days a week on site.

Key responsibilities

• Lead technical initiatives and set technical direction for meaningful parts of the roadmap, owning architecture and approach
• Work closely with Product and Design from the earliest conversations, shaping what gets built
• Own systems end to end, from problem definition through production rollout and long-term maintenance
• Talk directly with customers and help define how AI features are designed, built and run at scale
• Promote spec-driven development and build shared, reusable components and AI "skills" that other teams can use
• Build monitoring and quality tooling, and help ground AI features in trusted data

Required profile

• Solid depth in both backend and frontend engineering, with shipped production products
• Experience integrating LLM APIs into product features (not model training or fine-tuning)
• Technical and cultural leadership, able to push back on processes that do not serve the team
• Clear communication in English; Spanish is a plus

Required skills

• Ruby on Rails and React
• APIs and cloud platforms (AWS, Azure or GCP)
• System design

What we offer

• Office-first, flexible schedule with remote work options
• Competitive ESOP plan and private health insurance
• Wellness benefits, language classes, food discounts and pet-friendly office