AI Engineer (Up to £220k + equity)

Staff / Principal AI Engineer, AI Platform | Up to £220k + Equity | London, Hybrid. We’re working with a well-funded frontier AI company building the infrastructure used to train and evaluate increasingly capable AI agents. They create interactive software environments where agents can complete tasks, receive feedback and improve through experience. The platform is already being used in real training and research workflows with leading AI labs. They’re now scaling the core AI platform and hiring senior ICs to own major areas across model improvement, post-training, RL, evaluations and agent infrastructure. Role A deeply hands-on Staff / Principal position with significant technical ownership. You’ll define research and engineering direction while staying close to models, experiments and production systems. Responsibilities * Own major AI initiatives from research question through to production * Lead work across post-training, fine-tuning, RL and model evaluation * Build agent harnesses, sandboxed execution environments and feedback systems * Develop training-data, synthetic-data and curation pipelines * Design experiments, evaluation frameworks and measurable success criteria * Turn successful research into scalable, observable production systems Requirements * Strong hands-on experience training, fine-tuning or post-training ML models * Deep understanding of modern ML, RL, evaluation and model optimisation * Experience building agentic systems or AI infrastructure * Strong software engineering fundamentals and production-quality Python * Track record owning technically ambiguous, high-impact projects * Staff / Principal-level technical leadership while remaining an IC Tech Python, LLMs, RL, post-training, model evaluation, agents, synthetic data, distributed AI systems Location London, typically 2 days per week. Package Up to £220,000 base depending on experience, plus meaningful equity.