Senior Machine Learning Engineer

Senior Machine Learning Engineer 🌍 UK or Poland (Remote or Hybrid, it’s up to you!) 💰 Dependent on experience 📈 Be part of our success with the opportunity to join our company equity scheme Our Perks ❤️ Monthly Health & Wellness budget, increasing with length of service 📚 Annual Learning and Development budget, increasing with length of service 🤸🏽‍♂️ Flexible working in a choice-first environment - we trust the way you want to work! 🖥️ Work From Home Allowance 🌴 25 Holiday Days + your local bank holidays, plus an extra day for every year of service 🎂 Your birthday off 🍼 Enhanced Family Leave (UK Only), Fertility Leave, and Neonatal Leave ⚕️ Optional Healthcare Plan 🛟 Life & income protection (Location dependent) 🤝 Employee Assistance Programme (UK Only) 📈 The opportunity to share in the company’s success through options 🌆 If you’re in London, a dog-friendly office with great classes, events, and a rooftop terrace 🦸‍♀️ The Role 🦸‍♀️ Our mission is to help large successful brands like Uber, Amazon, Wise, HelloFresh (and more!) put their customers at the centre of everything they do. Using best-in-class tech in a fast-developing AI space, our Customer Experience Intelligence platform continuously analyses explicit and implicit feedback to enable our clients to identify what they should do next. We're hiring a Senior Machine Learning Engineer to join the team and help build and ship the next generation of that stack. 👉 What you'll be doing: Unlike many companies, we use our own custom models, specialised for customer feedback, across various parts of the stack: extraction, retrieval, reranking, summarisation, and sentiment analysis. We are also pragmatic and understand that the right solution can be a combination of off-the-shelf LLMs, bespoke fine-tuned models, and sometimes techniques that utilise no LLM at all. This means you will: - Train, evaluate, and iterate on ML models and agentic systems for customer feedback, including owning our custom fine-tuning pipelines. Run experiments end-to-end, track results rigorously, and make clear recommendations on what to ship, iterate, or retire. - Build and maintain LLM-powered features: retrieval pipelines, reranking systems, insight agents, data mining agents, and automated taxonomy generation. - Design and run robust evaluation frameworks: build test sets, define metrics, evaluate non-deterministic systems, handle class imbalance, and automate checkpoint comparisons. - Improve and extend semantic search and retrieval, evolving from embedding-based approaches toward more advanced methods. - Write production-quality code and collaborate closely with Engineering on productionisation, model serving, data pipelines, and monitoring. - Work with Product and Commercial teams to translate business needs into practical ML solutions, and support client evaluations and accuracy benchmarking. - Mentor team members, review code and research, and bring relevant advances from the literature into the product. 🧰 What you’ll need: - A deep working knowledge of transformer architectures. - Strong PyTorch skills, with the ability to write custom training loops, modify model architectures, and debug issues at the tensor level. Ideally, experience with parameter-efficient fine-tuning techniques such as LoRA - Extensive experience working with large-scale, messy real-world text data, including classification, extraction, embeddings, re-rankers, clustering, and search. - Experience in instruction fine-tuning and serving language models, familiarity with frameworks such as vLLM, DeepSpeed, or similar tools - A solid grounding in classical ML and statistics, and the judgement to choose simpler methods when they’re the right solution. - Practical experience building with GenAI and agentic patterns. - Excellent communication skills and confidence translating complex technical concepts for non-technical audiences (and vice versa!). - Technical curiosity and a keen interest in AI – a love of exp…