Senior Machine Learning Scientist

Stack

Responsibilities

• ▹Train, evaluate, and iterate on ML models and agentic systems for customer feedback, including owning 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, 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, supporting client evaluations and accuracy benchmarking
• ▹Mentor team members, review code and research, and bring relevant advances from the literature into the product

Requirements

• ▹A deep working knowledge of transformer architectures
• ▹Strong PyTorch skills, with the ability to write custom training loops, modify model architectures, and debug 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: classification, extraction, embeddings, re-rankers, clustering, search
• ▹Experience in instruction fine-tuning and serving language models, familiarity with frameworks such as vLLM, DeepSpeed or similar
• ▹A solid grounding in classical ML and statistics, and the judgement to choose simpler methods when appropriate
• ▹Practical experience building with GenAI and agentic patterns
• ▹Excellent communication skills, confident translating complex technical concepts for non-technical audiences and vice versa
• ▹Technical curiosity and a keen interest in AI, a love of experimenting
• ▹High ownership and initiative, able to identify problems, prioritise, and drive solutions forward

Nice to have

• ▹MSc/PhD in Computer Science, Machine Learning, Artificial Intelligence, Data Science, Computational Linguistics or a closely related STEM field
• ▹Experience with reinforcement learning techniques, such as with verifiable reward (RLVR)

Soft skills

What we offer

• ▹Monthly health & wellness budget, increasing with length of service
• ▹Annual learning & development budget, increasing with length of service
• ▹Flexible working in a choice-first environment
• ▹Work-from-home allowance
• ▹25 holiday days + local bank holidays, plus an extra day per year of service
• ▹Your birthday off
• ▹Enhanced family leave, fertility leave and neonatal leave (UK)
• ▹Optional healthcare plan
• ▹Life & income protection (location dependent)
• ▹Employee Assistance Programme (UK)
• ▹The opportunity to share in the company's success through options
• ▹Dog-friendly London office with great classes, events and rooftop terrace

About the company

Chattermill's mission is to help large successful brands like Uber, Amazon, Wise, and HelloFresh put their customers at the centre of everything they do. Its Customer Experience Intelligence platform continuously analyses explicit and implicit feedback using custom models specialised for customer feedback.