Sthenos

EFA GROUP comprises companies in Aerospace, Security, Defense, and Industrial Cooperation with a solid international presence. EFA GROUP currently employs more than 400 people, the majority of whom are engineers and scientists. Headquartered in Greece, the Group maintains a strong international presence across Europe (Cyprus, Belgium, Switzerland, Estonia, and Germany), Asia (Singapore, Indonesia, and South Korea), the Middle East (UAE), and the United States, serving customers in 34 countries worldwide. 

The GROUP  includes EFA VENTURES (Supply Chain Management and integrated services), AEROSPACE VENTURES (Industrial Participation and related services), SCYTALYS (Systems Integration and Software), ES SYSTEMS (MEMs & IoT Integration), EPICOS (Global Defense B2B Information Platform), UCANDRONE (Unmanned Systems), AETHER AERONAUTICS (Target Drones), STHENOS AI (Intelligence Solutions), THYREOS CYBER (cyber security), SUPERIOR AIR (aviation services and specialized aerial missions), SSMART (defense hardware - software production and services). 

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 

Sthenos AI is looking for 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. 

Key Responsibilities 

• Design and build the platform back end in Python (FastAPI or Django), including its core services and modules
• Own the data architecture: schema design, migrations, and data integrity across modules in PostgreSQL
• Build a robust authentication and role-based access control layer that handles sensitive business data correctly
• Design clean, well-documented APIs that the front end and third-party integrations consume
• Integrate LLM and AI services into workflows (document processing, summarization, agents) with proper guardrails, logging, and cost controls
• Build integrations with external systems (accounting, payroll, email, e-signature, etc.)
• Set up background job processing, audit logging, and observability
• Establish engineering standards: testing, code review, CI/CD, and documentation
• Work closely with the front end engineer and business stakeholders to translate operational processes into product 

Requirements

• 5+ years of back end engineering experience
• Proven experience designing and shipping a production system from scratch, not only extending existing ones
• Strong relational database skills: data modeling, query performance, migrations
• Deep understanding of API design, authentication (OAuth2/OIDC), and authorization patterns such as RBAC
• Experience handling sensitive data: security best practices, audit trails, GDPR awareness
• Hands-on experience integrating LLM APIs or building AI-assisted features in production
• Comfortable in a small team: pragmatic, self-directed, strong written communication 

Nice to Have 

• Experience building ERP, HRIS, CRM, or other internal business systems
• Experience with event-driven architecture or workflow engines
• Familiarity with RAG pipelines, vector databases, or agent frameworks
• DevOps 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 modeling
• Ability to work independently while collaborating effectively within a small team
• Passion for AI-driven technologies and for building platforms people rely on every day
• Structured and detail-oriented way of working, particularly around data integrity and security
• Pragmatic mindset: prefers simple, maintainable solutions over clever ones
• Openness to feedback and continuous improvement
• Good communication skills; able to explain technical concepts clearly to non-technical stakeholders
• Fluent in English, both written and spoken