LLM Data Researcher

ABOUT THE ROLE Join the founding research team at an AI company to investigate whether expert-authored datasets improve frontier language models and inform future product direction. The role focuses primarily on hands-on experimentation, with collaboration across clients, partners, and the data team. WHAT YOU'LL DO - Post-train models on curated datasets, measure performance changes, and diagnose cases where the data does not improve results. - Design and run evaluations of frontier language models across expert domains such as law, medicine, and finance. - Select and apply training approaches, including supervised fine-tuning, reinforcement learning, and preference-based methods. - Turn research findings into dataset specifications and product recommendations. - Share results through research papers, public benchmarks, and blog posts. WHAT WE'RE LOOKING FOR - A PhD in machine learning or NLP, completed or near completion, or an equivalent research record. - Hands-on experience with reinforcement learning environments for LLMs or RL-based LLM post-training, supported by research, code, or lab or industry work. - Experience personally post-training and evaluating LLMs end to end, including SFT, RLHF, RLVR, reward modeling, or preference optimization. - Experience designing or building robust LLM evaluations or benchmarks. - Early-career research experience, from a PhD nearing completion to a few years post-PhD. - Ability to communicate technical findings to research, operations, and non-technical audiences, and fluency with AI tools and coding agents. - Professional English; publications at leading ML or NLP venues or evaluation tooling experience are a plus. COMPENSATION & BENEFITS Competitive salary, equity, and relocation support are available. Salary range and visa sponsorship details were not provided. LOCATION Full-time, on-site in Barcelona, Catalonia, Spain. Relocation to Barcelona is expected if you are not already based there.