Senior AI Engineer – AI Platform - £150k + Equity

Senior AI Engineer – AI Platform - £150k + Equity London | Hybrid (1 - 2 days per week onsite) | £100 - 150k base + meaningful equity Our client is a fast-growing AI company building the infrastructure that helps AI learn from active experience. They create interactive, resettable digital environments, ranging from simple websites to complex enterprise applications, where AI agents can navigate software, complete tasks and learn through trial and error. Working closely with leading AI labs, the team is developing the systems, data and tooling required to train and evaluate increasingly capable AI agents. They're now looking for a Senior AI Engineer to take ownership of difficult AI and research-engineering problems and turn ambiguous questions into practical, high-impact solutions. What you'll be doing * Own challenging AI and research-engineering problems from the initial idea through experimentation, implementation and production. * Develop approaches for creating, curating and improving high-quality training data for advanced models and AI agents. * Develop AI agent harnesses, sandboxed environments and systems that connect models to interactive software tasks. * Prototype rapidly, establish what works through experimentation, then turn successful approaches into robust, observable production systems. * Take ownership of substantial technical projects over months, rather than working solely on isolated experiments or features. You'll likely have: * Hands-on experience fine-tuning or post-training models, rather than solely working with model APIs. * Strong foundations across modern AI/ML, including model training, optimisation and evaluation. * Practical experience with SFT, reinforcement learning, RLHF or related post-training techniques. * Strong Python skills and the software engineering depth to build clean, testable and reliable systems. * Experience owning meaningful technical outcomes and making trade-offs across research, data and engineering. London | Hybrid (1 - 2 days per week onsite) | £100 - 150k base + meaningful equity