Software Engineer

Software Engineer at Cala in Barcelona | JobFluent About Halcyon Labs From the creators of Vilynx - a Barcelona AI startup acquired by Apple - comes Halcyon Labs: a bold new venture redefining how information is verified and represented at massive scale. Based in Barcelona’s vibrant tech hub near Passeig de Gràcia, Halcyon Labs is building innovative AI systems focused on trust, accuracy, and impactful technology that challenges industry norms. Recently, Halcyon Labs was named by Creandum to their #EuroSeed50 list - highlighting the most promising early-stage startups in Europe - an honor that reflects the strong belief in our mission and team. We are a small, ambitious group dedicated to building real solutions with grit, heart, and a culture of authenticity. We are now growing our engineering team with 2–3 versatile Software Engineers who enjoy working across boundaries - backend, data, infrastructure, and applied AI. About the role 💡 We’re looking for generalist product engineers with depth. You might come from a Backend Engineering, Data Engineering, or applied ML background - but what matters most is your motivation to build across layers and solve complex problems end-to-end. This is not a pure Data role, nor a pure Backend role - it’s a high-impact engineering position for someone who enjoys working with multiple parts of the system. You’ll work closely with our core team to design, build, and scale systems that power large-scale AI-driven information verification and representation. What you’ll do 🛠️ - Design and build backend services using Python (FastAPI) - Develop and maintain scalable data pipelines (batch and streaming) - Architect data storage systems using SQL and NoSQL technologies (Postgres, Redis, Cassandra, graph databases) - Work with cloud infrastructure on AWS and containerized environments (Kubernetes) - Experiment with emerging AI engineering tooling (coding agents, MCP ecosystems, etc.) - Collaborate on system design and cross-functional architectural decisions - Contribute to a culture of clean, pragmatic, high-quality engineering Things we value 🔎 Background and/or motivation to work in one of the following: - Backend Engineering (Python, APIs, distributed systems) - Data Engineering (big data pipelines, storage systems, processing frameworks) - Applied ML Engineering (production-focused, not research-only) Technical stack we commonly work with: - Python - FastAPI or similar frameworks - AWS - Kubernetes - SQL and NoSQL databases (Postgres, Redis; Cassandra or graph databases are a plus) - Search systems or information retrieval is a nice to have - DevOps practices Profile: - Builders at heart: hackathons, side projects, open-source contributions, active GitHub are all highly appreciated - Curious about the AI ecosystem and modern developer tooling - Motivated to work across domains rather than in a narrow specialization - Comfortable in a fast-moving startup environment - C1+ level in either English or Spanish (fluency in either is acceptable) Diversity & Inclusion 🌍 We are intentionally building a diverse team. We strongly encourage applications from women, underrepresented groups in tech, and individuals from non-traditional or less represented backgrounds. Diverse perspectives are critical to building responsible AI systems. If you’re excited about the role but don’t meet every requirement, we’d still love to hear from you. Compensation & Work Model 💼 - Competitive salary - Stock options - Hybrid model: 3 days per week onsite - New office opening soon on Gran Via (Barcelona), with a full dedicated space for Halcyon Labs - Flexible benefits covering transport, meals, and health insurance Why Halcyon Labs? ✨ - Work alongside a founder with a proven track record in AI startups - Build foundational AI systems with an "AI for good" focus - High ownership, high autonomy, real technical challenges - Join at an early stage and help shape both technology and culture - A supportive, inclusive, and horizontal team environment Hiring Process – Conversation-Based (No Coding Tests) 🤝 - Initial chat with team member focused on experience and projects - System design interview with CTO (onsite preferred) - Cultural fit conversation with CEO - Offer #### Read full job description