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 Frontend Engineer to build the interface for our internal platform: the workspace where the entire company will do its daily work. You will own the front end architecture, build our design system, and turn complex operational workflows into interfaces people actually enjoy using. 

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

• Architect and build the platform front end in React and TypeScript from the ground up
• Create and maintain a design system and component library used across all platform modules
• Build complex, data-heavy interfaces: dashboards, tables with filtering and bulk actions, multi-step forms, approval flows, and document views
• Build AI-native UI patterns: chat and assistant interfaces, streaming responses, inline AI suggestions
• Own front end state management, data fetching, and caching strategy against the platform APIs
• Ensure quality across the board: accessibility, responsiveness, performance, and cross-browser support
• Set up front end tooling, testing, and CI standards
• Work directly with the back end engineer on API contracts and with stakeholders on UX for their workflows 

Requirements

• 5+ years of front end engineering experience in React
• Strong TypeScript and modern React (hooks, suspense, server-state libraries such as TanStack Query)
• Proven experience building large, data-dense business applications, not only marketing sites or simple SPAs
• Experience building or significantly contributing to a design system or shared component library
• Solid grasp of front end architecture: state management, routing, code splitting, performance profiling
• Good product and UX instincts; able to work from rough requirements without a full-time designer
• Comfortable in a small team: pragmatic, self-directed, strong written communication 

Nice to Have 

• Experience with AI product interfaces (chat UIs, streaming, optimistic updates)
• Experience with data visualization libraries
• Familiarity with Python back ends and API co-design
• Basic design skills (Figma) or close collaboration experience with designers
• Experience with internal tools, ERP, or B2B SaaS products 

Your Competencies 

• Strong analytical and problem-solving skills with a sharp eye for usability
• Ability to work independently while collaborating effectively within a small team
• Passion for AI-driven products and for crafting interfaces people enjoy using
• Structured and detail-oriented way of working: consistency, accessibility, and polish matter to you
• Pragmatic mindset: prefers simple, maintainable solutions over clever ones
• Openness to feedback and continuous improvement
• Good communication skills; comfortable discussing UX and technical trade-offs with stakeholders
• Fluent in English, both written and spoken