458 Best startup Jobs in Spain (December 2025) - page 4

Senior AI/ML Engineer - Founding Team

13 hours ago

Madrid

☀️ Accelerating the Energy Transition, One Algorithm at a Time TetraxAI is revolutionizing renewable energy infrastructure development, making it 100x faster and 10x cheaper through cutting-edge B2B SaaS powered by AI. Join our founding team of exceptionally experienced entrepreneurs: Marta: Energy M&A lawyer with +2GW in transactions under her belt Arnau: PhD in EECS, architected smart pricing algorithms at WalmartLabs Katya: Launched Amazon Flex across 4 countries, scaling operations from scratch Your Mission As a Founding Team member, you'll be responsible for designing, evaluating and improving the AI/ML models and agentic workflows that will enable the processing of millions of documents and terabytes worth of project information every day, helping developers and investors make better decisions in a shorter time. Core Responsibilities: Design, evaluate and debug agentic workflows. Train, evaluate and debug high performing ML models, including fine-tuning Large Language Models to specific domains. Maintain and operate software and its infrastructure with high availability. Develop and deploy high-throughput, big data data pipelines. Deep understanding of business requirements and of relevant technical literature to strike the best possible trade-offs. What We're Looking For Proven track-record of building scalable ML/AI products for document processing under strict privacy and security constraints . We don’t care as much about years of experience but about wealth of experience in challenging situations and verticals. Comfortable with trade-offs and with finding the right balance between best practices, debt and speed of execution on a case by case basis. We want folks that understand that there is no single best solution to all problems and that engineering is all about striking the right trade-offs. Strong data science and machine learning fundamentals . We believe that to fully harness the power of the current AI models, a strong understanding of the fundamentals of statistical learning is more important than ever. Passion for our mission of fighting climate change with clean tech. Being a founding team member is an extremely challenging endeavor - believing in our mission is the (renewable) fuel that will power us through tough times. Clear and rigorous communication . Building software at a startup is 90% communication (with stakeholders, with customers, with team members, with AI-assistants) to align, understand requirements and ideate an optimal solution. We are looking for engineers that enjoy collaboration and that understand that building complex systems is a team effort. ️ The TetraxAI Way At Tetrax, our culture is built around action, ownership, kindness and relentless focus on creating value for our customers . We’re a small, driven team solving hard problems—so how we work together matters just as much as what we’re building. These principles guide how we make decisions, collaborate, and grow: Obsess Over the Customer Our work starts and ends with the people we serve. We listen closely, ask questions, and design with empathy. If it doesn’t create value for our users, we don’t build it. Act Fast, Learn Faster We move quickly, experiment often, and don’t wait for perfect conditions. Progress beats perfection—and we learn by doing. Speed matters in business, especially when you’re building something new. Own the Outcome Everyone at Tetrax takes responsibility beyond their role. We don’t say “that’s not my job”—we dive in, take initiative, and follow through. We care deeply about the long-term success of what we’re building. Deliver Results Results matter. We set ambitious goals and hold ourselves accountable to them. We work with urgency, stay focused, and finish what we start—because impact only happens when ideas are executed. Strive for Excellence We take pride in the quality of our work. Whether it’s a product demo, a customer email, or a line of code—we push for high standards and constantly raise the bar for ourselves and each other. Work with Integrity We believe that how we work matters just as much as what we achieve. We treat others with respect, assume good intent, and communicate openly—even when it’s hard. We hold ourselves to high ethical standards and aim to create a culture where kindness, trust, and accountability go hand in hand. Why Join Us? Impact: Your code will directly accelerate renewable energy project financing, contributing to global decarbonization efforts Growth: Work directly with seasoned founders and gain hands-on experience in AI, energy, and climate tech Compensation: €60-80k salary + top-of-market equity package. Flexibility: Hybrid work model in beautiful Barcelona, 2.5-day/week in-person ‍‍‍ Family-friendliness : We have children and understand that even though this is a startup, first things come first. Flat-hierarchy: we encourage open communication, fast decision-making, and mutual respect. You’ll work directly with the founding team and have real ownership over your projects. Our hiring process We want to keep it nice and lean, while making sure both parties get to know each other well enough before we tie the knot! Our hiring process consist in 4 stages which may or may not follow this order: Initial phone screening (30' videocall) : Getting to know each other, your goals and constraints around availability, compensation, objectives. Technical take-home challenge (3h, to be completed in 72h) : A technical take home challenge that will serve as the basis for the following technical interviews. The take home can be scheduled at a time and date of your convenience and needs to be completed within 72h. Technical interview - take-home discussion (1h30 videocall): A chat with our CTO and an expert software engineer on architecture, system design, design patterns, best practices. Culture & values fit interview with our COO (1h videocall) Final interview with our CEO (45' videocall) We will strive to move fast and commit to giving feedback as soon as possible.

Startup jobs in Spain - Page 4

Popular jobs searches in Spain

Popular startup jobs locations