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.RoleA 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.ResponsibilitiesOwn major AI initiatives from research question through to productionLead work across post-training, fine-tuning, RL and model evaluationBuild agent harnesses, sandboxed execution environments and feedback systemsDevelop training-data, synthetic-data and curation pipelinesDesign experiments, evaluation frameworks and measurable success criteriaTurn successful research into scalable, observable production systemsRequirementsStrong hands-on experience training, fine-tuning or post-training ML modelsDeep understanding of modern ML, RL, evaluation and model optimisationExperience building agentic systems or AI infrastructureStrong software engineering fundamentals and production-quality PythonTrack record owning technically ambiguous, high-impact projectsStaff / Principal-level technical leadership while remaining an ICTechPython, LLMs, RL, post-training, model evaluation, agents, synthetic data, distributed AI systemsLocationLondon, typically 2 days per week. PackageUp to £220,000 base depending on experience, plus meaningful equity.