Senior Backend Engineer

Upside is a software consultancy built by engineers, for engineers. We partner with global companies to solve real, complex technical challenges. We’re deep into Applied AI and R&D, building both production-grade platforms for clients and our own open-source tools like Enthusiast (Agentic AI framework). We operate in a Forward-Deployed model. We don’t sit behind a wall of specs or wait for the tickets. We get into the trenches with the client, identify the actual challenges, and take full ownership of the solution. Our teams are small (3–9 people), autonomous, and cross-functional. What it means for you You'll work with a capable and driven team, and partner directly with senior business leaders on technical decisions, shaping systems - not just implementing them. You’ll have the autonomy to choose the right tools and the ownership to ensure the architecture performs under pressure.Your focus stays where it counts: mission-critical logic and high-impact experiments, not repetitive tasks and countless meetings. You’ll contribute to strategic open-source projects and build AI-driven solutions. Role Overview As a Senior Backend Engineer, you’ll be the backbone of our development efforts and a key driver of our engineering culture. You will design, build, and scale resilient systems for international clients while staying close to the code. We’re looking for someone who brings ready solutions rather than problems to solve, and treats the client’s product as their own. This isn't a short-term opportunity - we’re looking for a partner to grow with us, someone who thrives in a highly collaborative environment and proactively shares "lessons learned" to level up the entire team. Responsibilities Drive technical direction: Own the architecture and implementation of complex backend systems. Problem Solving: Identify systemic risks before they manifest and propose clear, actionable ways to bypass them. Consulting: Work directly with stakeholders to translate business needs into scalable technology. Mentorship: Share your observations and "lessons learned" to help the whole team level up. AI Integration: Identify where Applied AI can actually improve a product and lead the implementation. Experience: 5+ years of building web applications (preferably in Python frameworks). Background: Completed university degree in computer science, data science or similar field Architecture: Deep understanding of monoliths, microservices, and messaging patterns. Databases: Expert knowledge of PostgreSQL and performance optimization at scale. Infrastructure: Practical experience with CI/CD, Docker, and AWS/GCP. Mindset: Proactive, technology-driven, and ready to experiment. AI-Native: You use tools like Claude or Cursor to move faster. English: Fluent (C1) for direct client collaboration. Our Tech Stack: Python, PostgreSQL, AWS, Docker, Kubernetes. Ruby is present in some of our projects but we are Python first. Value Proposition Built for the long run We hire for the company, not just a project - looking for passion driven engineers who want to grow with Upside over time Small teams, real accountability. 3-9 people per engagement. We're small by design. That means your decisions carry weight and you are visible. Mission-critical work: We handle complex projects that move the needle for international brands. Our clients are scaling companies, established international brands, and large institutions. The systems you build will be under real load, with real stakes. Real Ownership: You take part in the decision making process on technology and implementation..You’re empowered to take initiative, experiment, and drive solutions that create real impact. No Micromanagement: We trust you to own your work and deliver outcomes - no unnecessary oversight. Collaborative R&D: Contribute to targeted Open-source projects and internal AI research. Growth through challenges: Complex problems and direct client exposure means you’ll grow by action. Applied AI as a first-class discipline. We don't bolt AI onto projects as an afterthought. You'll identify where it genuinely moves the needle and lead the implementation - on client work and on our own open-source tooling. The tools you want, without the approval process. If something makes you faster or sharper, we want you using it. Transparent progression path. We have defined engineering levels with clear criteria - you'll know exactly what each role looks like, and what it takes to get from one to the other. No ambiguity, no waiting for someone above you to move on. Compensation & Location Location: On-site in Kraków; Hybrid; remote from anywhere in Poland with regular team on-sites. Salary: Senior Engineer: 20 800 - 25 900 PLN net + VAT Lead Engineer: >26 500 PLN net + VAT If you’d like to understand more about how we work or read about the recruitment process in detail, feel free to explore our handbook . If something important to you isn’t mentioned - share your thoughts with as at careers@upsidelab.io