Principal Generative AI Engineer

ABOUT MOTORWAY Motorway is the UK’s fastest-growing used car marketplace - our online-only platform connects private car sellers with thousands of verified dealers nationwide, ensuring everyone gets the best deal. Founded in 2017, our award-winning, technology-led approach has redefined the experience of selling a car. Motorway is backed by some of the world’s leading technology investors, having raised £143 million in Series C funding. This is a unique opportunity to join a fast-growing scale-up at a crucial phase of growth and help change an industry for the better. ABOUT THE TEAM GenAI Engineering sits within Motorway's Data and AI function, alongside Machine Learning and the Machine Learning Data Platform. The team owns the GenAI features that shape how buyers and sellers experience the marketplace, spanning agentic workflows in the customer experience and LLM-powered tooling for our dealer network. Over the next two years the function scales from shipping AI features into running a serious GenAI platform. This hire is the technical authority who'll help shape that platform, working closely with engineering leadership across Data and AI and the wider Engineering org. ABOUT THE ROLE This is the most senior individual contributor role on Motorway's GenAI engineering ladder (IC5 / Principal). You'll report to the Director of Data and AI, advising the CPO and the wider exec on AI technical strategy. The remit is the trajectory of GenAI engineering at Motorway over a two-to-three-year horizon: the architecture, the standards and the strategic bets that no single team can absorb on its own. You'll set architectural direction across the GenAI surface area, hold sign-off on materially complex AI systems, and have the credibility to veto implementations that don't meet our agreed technical, safety or quality bar. You'll shape the high-stakes calls on vendor strategy, model selection, build-vs-buy on platform infrastructure, and our responsible-AI posture, providing the technical rationale that lets the Director of Data and AI and the wider exec land those calls with confidence. This is still a hands-on engineering role: you'll design and build the hardest single pieces of work directly, write production code on the systems that matter most, and pair with senior engineers on the architectural decisions that will outlast specific features. You won't own all AI usage at Motorway, you won't own overall AI strategy, and you won't hold budget for AI infrastructure, but you'll contribute meaningfully to all three, and you'll define how GenAI is built and evaluated here. This is a newly-created role and a greenfield opportunity. The technical bets you make will sit behind Motorway's most strategic AI initiatives, including ones not yet started. AI engineering choices at this level shape unit economics for years. IN THIS ROLE, YOU WILL: - Set the overarching architecture for GenAI at Motorway, including reusable patterns for prompt design, RAG (hybrid retrieval, chunking, semantic caching), agent orchestration, evaluation frameworks (LLM-as-judge, golden datasets, adversarial prompts), guardrails and observability that other teams build on - Design and build the hardest single pieces of work directly, taking on the problems nobody else is well-placed to solve and leading our highest-risk, highest-reward technical bets across the GenAI surface area - Hold sign-off on architectural decisions for materially complex GenAI systems, with the credibility to veto implementations that don't meet our agreed technical, safety or quality bar - Advise the Director of Data and AI on build-vs-buy calls for AI infrastructure (vector stores, eval platforms, AI gateways, model routers, agent frameworks), and own the technical rationale behind them - Drive cost, latency and throughput optimisation across our production GenAI systems, with the trade-offs documented and explicit - Define our principles for emerging paradigms, including multi-agent protocols, mu