ML Engineer for Lumen Enterprise Models (London, Equity)

Cosine; Greater London; On-site; GBP 90,000 - 150,000; Full time

Job summary

Cosine, based in London, is hiring a Machine Learning Engineer for Lumen Enterprise models (SWE-focused LLMs). The role is in-office in London with ASAP start. The engineer will train and improve models across pre-training, SFT and RL stages, profiling and optimizing performance while maintaining high software quality.

Equity options may be discussed. You will work with research, infrastructure and product teams to scale training, evaluate data and environments, and push the boundaries of

Qualifications

• Strong experience training deep-learning models in a production or research environment.
• Deep practical experience with PyTorch or a comparable framework.
• Experience with distributed training and multi-GPU systems (FSDP, Deepspeed, ...)
• Strong software-engineering fundamentals and a high bar for correctness and maintainability.
• Clear communication and the ability to explain technical trade-offs.
• Experience with large language models is important. You should have worked meaningfully on at least one of, pre-training, SFT, preference optimisation, RLHF or RLVR.

Responsibilities

• Work across the full training lifecycle, running pre-training, supervised fine-tuning and reinforcement-learning experiments.
• Optimize training methods at scale on frontier models.
• Diagnose and fix performance bottlenecks and communication overhead in distributed training environments.
• Train models on long-context, multi-file and repository-level tasks.
• Develop RL and RLVR loops using signals from execution, tests, linters, static analysis and other engineering feedback, turning fresh ideas into scalable, reproducible code.
• Investigate model failure modes such as poor planning, brittle fixes, reward hacking and regressions.
• Collaborate with infrastructure, platform and data teams.

Skills

Deep learning

Distributed training

Software engineering fundamentals

Communication

LLMs

Tools

PyTorch

Deepspeed

Job description

Cosine, based in London, is hiring a Machine Learning Engineer for Lumen Enterprise models (SWE-focused LLMs). The role is in-office in London with ASAP start. The engineer will train and improve models across pre-training, SFT and RL stages, profiling and optimizing performance while maintaining high software quality.

Equity options may be discussed. You will work with research, infrastructure and product teams to scale training, evaluate data and environments, and push the boundaries of