Senior Research Engineer – Production AI Systems London | In-office | Up to £300k base significant equity About Our Client Our client is a very well-funded AI startup solving some of the hardest problems in production large language models. They're building systems that reliably handle complex, multi-step reasoning tasks at massive scale. Their team combines talent from top-tier quantitative trading firms, leading AI research labs, and Big Tech. Backed by tier-one venture capital, they ship fast, maintain exceptionally high technical standards, and operate as an in-office team in London. The Role They're hiring a Senior Research Engineer to build and deploy core AI models from conception through production. You'll work on genuinely hard, unsolved problems: building LLMs that reason reliably across long contexts, maintain coherent state over extended interactions, and make sound decisions under uncertainty – all whilst serving millions of requests with strict latency requirements. Hard Problems You'll Tackle Multi-turn reasoning and memory – Models that maintain coherent state across complex, extended interactions Production reliability at scale – Consistent, accurate behaviour serving millions of daily requests with sub-second latency Novel post-training methods – Training approaches optimised for real-world task completion, not benchmarks Real-time evaluation and orchestration – Systems that monitor quality and adaptively route between models in production Long-horizon task decomposition – AI systems that autonomously break down and execute multi-step problems What You'll Bring 5 years AI/ML engineering or research experience with production systems Hands-on post-training experience (RLHF, DPO, or similar) and deployed LLMs in production Strong Python and modern ML tooling (PyTorch/JAX, training infrastructure, evaluation pipelines) Track record shipping research from prototype to production impact Comfortable owning work end-to-end: architecture to data pipelines to production integration Why Join Work on genuine research problems that ship to production within weeks Collaborate with exceptional engineers from elite quant firms, frontier AI labs, and top tech companies Own multi-quarter initiatives and shape the research roadmap Up to £300k base significant equity In-office in London with some of Europe's best AI talent For more information, or a discreet chat regarding the market/similar roles, please get in touch: James@durlstonpartners.com