Senior Backend Engineer

About Sthenos AI Sthenos AI is the AI developer of EFA Group, building intelligent, mission-ready solutions for defense and aerospace. With deep expertise in Command-and-Control (C2), cyber defense, computer vision, and autonomous systems, we design and deploy secure, field-proven AI that enhances operational efficiency and situational awareness. As part of a leading European defense ecosystem, we bring scalable innovation where it matters most - in the theater of operations. Internally, we are building a unified operations platform: a single system through which the entire company will run its daily work, with AI woven through every workflow. We have validated the concept with a working prototype and are now assembling a small senior team to build the production platform properly, from the ground up. The Role We are hiring a Senior Backend Engineer to design and build the core of our internal platform: the data models, APIs, permissions system, and integrations that every business function will run on. You will own back end architecture decisions and set the standards the rest of the team builds against. This is a greenfield build with an unusual scope: one platform, many domains, designed for AI-native workflows from day one. You will be one of the first engineering hires, with real influence over architecture, tooling, and engineering culture. The prototype exists to learn from, not to maintain. What You Will Do Design and build the platform back end in Python (FastAPI or Django), including its core services and modulesOwn the data architecture: schema design, migrations, and data integrity across modules in PostgreSQLBuild a robust authentication and role-based access control layer that handles sensitive business data correctlyDesign clean, well-documented APIs that the front end and third-party integrations consumeIntegrate LLM and AI services into workflows (document processing, summarization, agents) with proper guardrails, logging, and cost controlsBuild integrations with external systems (accounting, payroll, email, e-signature, etc.)Set up background job processing, audit logging, and observabilityEstablish engineering standards: testing, code review, CI/CD, and documentationWork closely with the front end engineer and business stakeholders to translate operational processes into product What We Are Looking For 5+ years of back end engineering experienceProven experience designing and shipping a production system from scratch, not only extending existing onesStrong relational database skills: data modeling, query performance, migrationsDeep understanding of API design, authentication (OAuth2/OIDC), and authorization patterns such as RBACExperience handling sensitive data: security best practices, audit trails, GDPR awarenessHands-on experience integrating LLM APIs or building AI-assisted features in productionComfortable in a small team: pragmatic, self-directed, strong written communication Nice to Have Experience building ERP, HRIS, CRM, or other internal business systemsExperience with event-driven architecture or workflow enginesFamiliarity with RAG pipelines, vector databases, or agent frameworksDevOps skills: Docker, IaC, cloud deployment (AWS, GCP, or Azure)Experience mentoring engineers or leading a small team Your Competencies Strong analytical and problem-solving skills, especially in system design and data modelingAbility to work independently while collaborating effectively within a small teamPassion for AI-driven technologies and for building platforms people rely on every dayStructured and detail-oriented way of working, particularly around data integrity and securityPragmatic mindset: prefers simple, maintainable solutions over clever onesOpenness to feedback and continuous improvementGood communication skills; able to explain technical concepts clearly to non-technical stakeholdersFluent in English, both written and spoken