Back End Developer

CyberproAI is looking for a highly experienced Senior Backend Engineer with strong, hands-on Python expertise to join our growing engineering team in Warsaw. This is a role for a senior engineer who loves solving complex technical challenges, designing scalable systems and building robust products that operate in real-world environments. You will work closely with engineering, product and AI teams to design and develop backend services, APIs and data-driven systems that are scalable, reliable and built to last. We are looking for someone who is not only an excellent Python developer, but also thinks architecturally, takes ownership and cares deeply about engineering quality. What You'll Do Design, build and maintain scalable backend applications and services using Python Develop robust REST APIs, microservices and backend integrations Own backend features from architecture and design through development, testing and production Work on complex, data-intensive systems and high-volume backend workflows Collaborate closely with Product, AI, Frontend, QA and DevOps teams Participate in architectural decisions and help shape technical direction Improve system performance, scalability, reliability and maintainability Write clean, efficient and well-tested production code Conduct code reviews and contribute to engineering best practices Troubleshoot and resolve complex production issues Mentor other developers and share technical knowledge across the team Continuously evaluate new technologies and improve development practices What You'll Bring 5+ years of professional backend development experience Strong and recent hands-on Python experience Excellent understanding of backend architecture and software engineering principles Experience developing production-grade APIs and microservices Strong experience with FastAPI, Flask or Django Experience with relational databases such as PostgreSQL Experience with technologies such as MongoDB, Redis, Kafka or RabbitMQ Strong understanding of distributed systems and asynchronous programming Experience with Docker Experience working with AWS, Azure or GCP Familiarity with Kubernetes and containerized production environments Strong understanding of CI/CD, automated testing and modern engineering workflows Strong problem-solving and debugging abilities Excellent English communication skills What Will Make You Stand Out Experience working on AI, machine learning or data-intensive products Experience integrating AI or LLM services into production backend systems Strong experience with FastAPI and asynchronous Python Proven system design and architecture experience Experience building systems operating at significant scale Strong Kubernetes experience Experience with event-driven or distributed architectures Previous experience in cybersecurity, SaaS or complex B2B technology products Open-source contributions or strong personal technical projects Experience mentoring or technically leading other engineers The Person We're Looking For You are a senior engineer who still loves to code. You can take a complex problem, understand the bigger architectural picture and then get hands-on and build the solution. You care about quality, performance and clean design, but you also understand the importance of delivering. You are curious, independent and comfortable taking ownership. When something breaks, you investigate it. When something can be built better, you improve it. And when the team faces a difficult technical challenge, you are one of the people everyone wants in the room. If Python is your language, backend engineering is your craft and building complex products is what excites you , we would love to hear from you.