ML Engineer at Cosine.sh

Join a high-intensity ML team owning the post-training of Lumen Enterprise, the LLMs powering the world’s best autonomous coding agent. You will drive SFT, RL, and continued pretraining to push state-of-the-art performance on complex software engineering tasks. This role offers direct impact on a product used by global enterprises.

• Transform open-source base models into high-performance SWE agents through supervised fine-tuning and advanced reinforcement learning (PPO, GRPO, or DPO).
• Design and execute large-scale training experiments on multi-node clusters, optimizing for long-context stability and tool-use reasoning.
• Build and iterate on automated RL loops where models are rewarded for successfully running tests, linters, and static analysis on real-world codebases.

• 3-5+ years of experience training deep learning models in production with deep proficiency in PyTorch distributed primitives like FSDP and DDP.
• Proven track record of training large-scale models (≥70B parameters) and implementing complex RLVR systems for LLM alignment.
• Strong software engineering background with the ability to write production-grade Python and a focus on data quality and sampling strategies.

• Direct ownership of post-training for Genie, a SOTA coding agent that achieved a 72% score on OpenAI’s SWE-Lancer benchmark.
• Work at the technical frontier with multi-node GPU clusters, large-scale MoE architectures, and long-context training on proprietary software-engineering reasoning data.
• Join a small, elite 4-person ML team reporting directly to the CEO, where your training runs ship immediately to real-world enterprise users.