Backend Engineer

Cala is looking for a Backend Engineer with 4+ years of experience to build the systems behind AI-driven information verification at scale 🚀 The team behind Vilynx, a Barcelona AI startup that Apple acquired, founded Cala. They're building a verified knowledge graph for AI agents, and they're looking for someone who is strong in backend work (Python, APIs, distributed systems) and also enjoys working on data, infrastructure and applied AI. 📍 Hybrid in Barcelona (3 days/week at their new office on Gran Via) 💰 Competitive salary + stock options 🏝️ Perks: flexible benefits for transport, meals and health insurance, plus a hiring process built on conversations with no coding tests It's a good opportunity for someone who likes owning systems end to end and wants to join an early-stage AI company. About Cala AI From the creators of Vilynx - a Barcelona AI startup acquired by Apple - comes Cala AI: 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, Cala AI is building innovative AI systems focused on trust, accuracy, and impactful technology that challenges industry norms. Recently, Cala AI 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 an experienced Backend Engineer who enjoys working across boundaries - backend, data, infrastructure, and applied AI. About the role 💡 We're looking for an experienced backend engineer with depth. You'll come from a Backend Engineering background - Python, APIs, distributed systems - but what matters most is your motivation to build across layers and solve complex problems end-to-end. Backend is your anchor, but this is a high-impact engineering position for someone who enjoys working with multiple parts of the system rather than in a narrow specialization. You'll work closely with our core team to design, build, and scale the backend systems that power large-scale AI-driven information verification and representation. What you'll do 🛠️ Design and build backend services using Python (FastAPI)Architect data storage and retrieval systems using SQL and NoSQL technologies (Postgres, Redis, Cassandra, graph databases)Develop and maintain scalable pipelines (batch and streaming)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 decisionsContribute to a culture of clean, pragmatic, high-quality engineering Things we value 🔎 Strong background in: Backend Engineering (Python, APIs, distributed systems) Technical stack we commonly work with: PythonFastAPI or similar frameworksAWSKubernetesSQL and NoSQL databases (Postgres, Redis; Cassandra or graph databases are a plus)Search systems or information retrieval is a nice to haveDevOps practices Profile: 4+ years of hands-on backend engineering experience, with real depth - you've gone deep, not wide and shallowAble to reason about and justify your technical decisions: pros, cons, why A over BBuilders at heart: hackathons, side projects, open-source contributions, active GitHub are all highly appreciatedCurious about how things work end-to-end, including the parts adjacent to your own - infrastructure, data, the systems your code runs onCurious about the AI ecosystem and modern developer toolingComfortable in a fast-moving startup environmentC1+ 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 salaryStock optionsHybrid model: 3 days per week onsiteNew office on Gran Via (Barcelona), with a full dedicated space for Cala AIFlexible benefits covering transport, meals, and health insurance Why Cala AI? ✨ Work alongside founders with a proven track record in AI startupsBuild foundational AI systems with an "AI for good" focusHigh ownership, high autonomy, real technical challengesJoin at an early stage and help shape both technology and cultureA supportive, inclusive, and horizontal team environment Hiring Process – Conversation-Based (No Coding Tests) 🤝 Initial chat with team member focused on experience and projectsSystem design interview with CTO (onsite preferred)Cultural fit conversation with CEOOffer About JobFluent 😍 ES - ¿QUÉ SOMOS? JobFluent es un híbrido entre una plataforma de empleo tecnológico de calidad y un equipo de asesores que te ayudan a crecer en tu carrera. Nuestro objetivo es que la vida de nuestros usuarios cambie a mejor y que el proceso de cambio (normalmente estresante) sea lo más FLUIDO y agradable posible. Somos conocidos por:️ Trato humano: nuestro equipo siempre está preparado para ayudarte de forma honesta y personalizada. Sin spam: primero te escuchamos y sólo después te sugerimos oportunidades relevantes y validadas que encajen con tus intereses e inquietudes. Acompañamiento: te damos consejos y te apoyamos durante todo el proceso de selección para aumentar tus probabilidades de éxito. Experiencia del candidato: esto es lo que nos mueve! Nos rebelamos contra la falta de feedback y otras malas prácticas demasiado habituales en nuestro mundo. EN - WHO WE ARE JobFluent is a hybrid between a quality tech job platform and a team of advisors who help you grow your career. Our goal is to make our users' lives change for the better and to make the (usually stressful) job search process as FLUENT and enjoyable as possible. We are known for:️ Human treatment: our team is always ready to help you in an honest and personalized way. No spam: first we listen to you and only then do we suggest relevant and validated opportunities that match your interests and concerns. Coaching: we give you advice and support you throughout the selection process to inc rease your chances of success. Candidate experience: this is what drives us! We rebel against the lack of feedback and other bad practices that are all too common in our world.