Senior Software Engineer (Fullstack)

Senior Software Engineer (Fullstack) About Us: Luzia is Europe’s fastest-growing AI consumer company, redefining conversational AI with cutting-edge large language models and an unparalleled user experience. With a strong and rapidly expanding presence in Brasil, we’re on a mission to make Luzia the go-to AI personal assistant, empowering millions of users to simplify and enhance their everyday lives. At Luzia, we ship fast: keep it simple, learn from every experiment, own outcomes, and build what our users need. We thrive in a fast-paced environment and expect everyone to use AI daily, automating the routine and amplifying creativity, because using AI isn’t optional; it’s how we win. ⚡ Hypergrowth startup with 80M+ users worldwide in under 3 years. 🌎Latin America as a core market with more than 60% of our user base. 🚀Backed by top-tier investors (Khosla Ventures, Prosus Ventures, A-Star, Monashees and more) . As a Fullstack Engineer, you’ll join our engineering team in Madrid, driving the development of scalable, high-impact solutions that power our AI-driven products. You don’t just implement features - you help shape how AI feels as a product. We’re looking for engineers who care about craft, interaction, and user experience, and who enjoy experimenting with new ideas. The best candidates for this role often build side projects, prototype new interfaces, explore emerging AI capabilities, or experiment with creative app experiences. What You’ll Do Build magical AI product experiences - Design and implement fast, intuitive, and engaging experiences that make AI feel natural and useful. Work closely with product and design to explore new interaction patterns, prototype ideas quickly, and turn cutting-edge AI capabilities into simple experiences that millions of users enjoy. Ship across the stack - Build and maintain backend services in Python and production-grade frontends in TypeScript and Next.js. Move fluidly between layers, owning features end to end. Architect scalable backend systems - Design and maintain backend services and APIs that power real-time AI interactions at scale. Ensure performance, reliability, and cost-efficiency as we grow rapidly across markets. Move fast, ship often - Operate with high ownership and urgency. Prototype quickly, validate with users, and iterate based on real-world feedback. Use modern AI-assisted development tools to accelerate development cycles while maintaining strong engineering quality. Collaborate across AI, product & growth - Work cross-functionally with AI engineers, product managers, designers, and growth teams to translate experimentation and insights into production-ready systems. Raise the technical bar - Write clean, maintainable, well-tested code. Contribute to architecture decisions, improve developer experience, and help establish best practices that enable the team to scale. Think in systems, not just tickets - Anticipate bottlenecks before they happen - whether in performance, UX, cost, or scalability. Proactively improve observability, reliability, and infrastructure as we scale. Mentor & lead by example - Provide thoughtful code reviews, support other engineers, and help shape a strong engineering culture centered around ownership, craftsmanship, and impact. What We’re Looking For +5 years of experience as a software engineer building and shipping production systems used by real users Strong backend experience in Python Strong frontend experience in TypeScript and Next.js, with an eye for usability, performance, and interaction design Hands-on experience building AI agents end-to-end - including tool use, orchestration, evaluation, and shipping them to production Experience building or integrating AI/LLM-powered features in consumer-facing products Curiosity about working across the stack, including backend services and APIs that power mobile experiences Comfort working in fast-paced startup environments with ambiguity and rapid iteration Strong product intuition: you care deeply about how things feel for users, not just how they are implemented Experience building systems or applications used by large numbers of users Ownership mindset: you see problems, take initiative, and drive solutions end-to-end Interest in AI-assisted software development, modern developer tooling, and experimenting with new ways of building products Nice to have Experience with LangGraph and/or LangChain Working model This is a hybrid role based in our Madrid office - you’ll combine working from our office and working from home Equal opportunity Luzia is an equal opportunity employer. We hire based on what you build and how you think. Ready to build with us? Apply via the link below. We read every application Department Backend Locations Madrid Office Remote status Hybrid