Full Stack Engineer - AI Systems

Full Stack Engineer, AI Systems Location: United Kingdom | Hybrid / Flexible Highly competitive package + equity We are working with a well-funded AI startup building its core technical team from the ground up, and are looking for an exceptional Full Stack Engineer to build the product layer of a new generation of AI-powered applications. This is not a conventional web development role or a position focused on adding a chatbot to an existing product. You will build production-grade systems in which AI can understand objectives, interact with external tools, retain context and reliably complete complex workflows across multiple steps. You’ll join at an unusually early stage, work alongside the founding technical team and have a genuine voice in how the product, architecture and engineering standards evolve. Rather than owning only one part of the stack, you will take features from initial idea through frontend, backend and AI integration into production. The Opportunity You will sit at the intersection of product engineering, backend systems, frontend development and applied AI. Your remit will include: Building end-to-end product features across frontend, backend and AI integrationsDesigning agent workflows involving planning, tool use, memory, failure handling and recoveryIntegrating large language models and external services into reliable production systemsBuilding user experiences for real-time AI interactionsImplementing streaming responses, partial results, loading states, retries and fallbacksDeveloping APIs and backend services that support long-running and multi-step workflowsDesigning systems that maintain context across tools, tasks and user sessionsImproving latency, responsiveness and overall application performanceBuilding monitoring, tracing and observability into AI-powered workflowsInvestigating real-world failure modes and continuously improving system reliabilityWorking closely with machine learning, backend, product and design teamsMaking pragmatic technical decisions and shipping improvements quicklyEstablishing reusable patterns for integrating models, memory and external tools You may work with technologies including: Next.js | React | TypeScript | Node.js | Python alongside: OpenAI | Anthropic | Open-source LLMs | SQL | NoSQL | Docker | Kubernetes What We’re Looking For We’re interested in people who have: Strong professional experience across both frontend and backend engineeringBuilt and shipped complete product features into productionStrong knowledge of modern frontend application developmentSolid experience designing backend services, APIs and data integrationsExperience working with LLMs, RAG systems, agents or AI-powered applicationsA good understanding of system design and scalable application architectureExperience building responsive or real-time user experiencesAn understanding of reliability, observability, latency and production debuggingThe ability to handle ambiguity and make sensible engineering trade-offsThe confidence to take ownership of features from idea through to productionA high level of curiosity, initiative and personal responsibilityComfort working in a small, fast-moving and highly collaborative teamExperience with sophisticated agent systems is valuable, but we are also interested in exceptional full stack engineers who have built complex production products and can quickly develop deeper expertise in AI-native application development. Why Join? You would be joining the founding technical team, not a large and established engineering department. That means the features, abstractions and technical decisions you make now can become the foundations upon which the product is built for years. You’ll have significant technical autonomy, direct exposure to leadership, equity participation and the opportunity to see your work translate directly into a user-facing AI product intended to operate at global scale. The ambition is to build AI experiences that move beyond simple chat and become proactive, persistent and dependable—helping users complete real tasks across tools and workflows with dramatically less effort. For someone who enjoys working across the entire product, solving difficult technical problems and having genuine influence over what is built, this is an unusually strong opportunity.