Senior Machine Learning Scientist

About the role

Chattermill helps leading brands such as Uber, Amazon and HelloFresh put customers at the centre of every decision. We are looking for a Senior Machine Learning Scientist to design, build and ship the next generation of our Customer Experience Intelligence platform.

Key responsibilities

• Train, evaluate and iterate on custom ML models and agentic systems for customer feedback, including managing fine‑tuning pipelines.
• Build and maintain LLM‑powered features such as retrieval pipelines, reranking systems, insight agents and automated taxonomy generation.
• Design robust evaluation frameworks, create test sets, define metrics and automate model checkpoint comparisons.
• Write production‑quality code, collaborate with engineering on model serving, data pipelines and monitoring.
• Partner with product and commercial teams to translate business needs into practical ML solutions and support client evaluations.

Required profile

• Deep working knowledge of transformer architectures and strong PyTorch expertise.
• Extensive experience with large‑scale, messy text data (classification, extraction, embeddings, re‑ranking, clustering, search).
• Proven ability to build and serve instruction‑fine‑tuned language models using frameworks such as vLLM or DeepSpeed.
• Solid grounding in classical machine learning, statistics and the judgement to choose simpler methods when appropriate.

Required skills

• Transformer architectures
• PyTorch
• LoRA (parameter‑efficient fine‑tuning)
• Large‑scale text data processing
• Instruction fine‑tuning of LLMs
• vLLM / DeepSpeed
• Classical machine learning
• Statistics
• Generative AI and agentic patterns

What we offer

• Equity scheme and option to share in company success
• Monthly health & wellness budget, increasing with tenure
• Annual learning & development budget
• Flexible working – remote or hybrid
• Work‑from‑home allowance, 25 holiday days plus local bank holidays
• Enhanced family leave, fertility and neonatal leave (UK only)
• Optional healthcare plan, life & income protection, employee assistance programme
• Dog‑friendly London office with rooftop terrace