Machine Learning Engineer at Cosine.sh

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Machine Learning Engineer Company Description: Cosine.sh is pioneering AI for software engineering, building advanced open-source-based models that empower developers with intelligent, real-world coding capabilities.

Job Description: Join Cosine.sh as a Machine Learning Engineer and lead large-scale training of Lumen Enterprise models-our flagship software engineering LLMs. You will drive state-of-the-art performance through supervised fine-tuning and reinforcement learning, operating close to the metal with PyTorch, distributed systems, and long-context architectures. This is a high-impact role where your work will directly shape the capabilities engineers depend on daily.

Location: London, UK

Why this role is remarkable:

• Directly influence the next generation of Lumen Enterprise SWE models used by engineers every day.
• Operate at real scale: modern open-source models, long-context training, MoE architectures, and multi-node GPU clusters.
• A true full-stack ML engineering role combining PyTorch, distributed systems, data pipelines, RL design, and MLOps.

What you will do:

• Transform open-source base models into high-performance Lumen Enterprise SWE agents using supervised fine-tuning and RL.
• Design and execute large-scale training experiments on multi-node GPU clusters, including long-context and MoE training.
• Build and refine large-scale RL loops where models write code, run tools/tests, and receive reward signals to improve performance.

The ideal candidate:

• 3-5+ years of experience training deep learning models in production environments.
• Deep proficiency with PyTorch and strong hands-on experience with torch.distributed for multi-GPU and multi-node training.
• Experience training large sequence models or LLMs (70B+ parameters), with practical understanding of scaling challenges.

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