Senior Frontend 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 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. What You Will Do Architect and build the platform front end in React and TypeScript from the ground upCreate and maintain a design system and component library used across all platform modulesBuild complex, data-heavy interfaces: dashboards, tables with filtering and bulk actions, multi-step forms, approval flows, and document viewsBuild AI-native UI patterns: chat and assistant interfaces, streaming responses, inline AI suggestionsOwn front end state management, data fetching, and caching strategy against the platform APIsEnsure quality across the board: accessibility, responsiveness, performance, and cross-browser supportSet up front end tooling, testing, and CI standardsWork directly with the back end engineer on API contracts and with stakeholders on UX for their workflows What We Are Looking For 5+ years of front end engineering experience in ReactStrong 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 SPAsExperience building or significantly contributing to a design system or shared component librarySolid grasp of front end architecture: state management, routing, code splitting, performance profilingGood product and UX instincts; able to work from rough requirements without a full-time designerComfortable 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 librariesFamiliarity with Python back ends and API co-designBasic design skills (Figma) or close collaboration experience with designersExperience with internal tools, ERP, or B2B SaaS products Your Competencies Strong analytical and problem-solving skills with a sharp eye for usabilityAbility to work independently while collaborating effectively within a small teamPassion for AI-driven products and for crafting interfaces people enjoy usingStructured and detail-oriented way of working: consistency, accessibility, and polish matter to youPragmatic mindset: prefers simple, maintainable solutions over clever onesOpenness to feedback and continuous improvementGood communication skills; comfortable discussing UX and technical trade-offs with stakeholdersFluent in English, both written and spoken