Member of Technical Staff - Post-Training

OUR MISSION Reflection is a research lab making intelligence open and accessible for everyone to use, customize, and build on. We build open models that let anyone control their intelligence and help shape the future of AI. Our mission: make intelligence open and accessible to all. ABOUT THE ROLE - Build systems that transform powerful pre-trained models into aligned and general agents. - Drive research and engineering initiatives that push the frontier of post-training, from data curation to large-scale optimization. - Develop data generation pipelines, reward models, reinforcement learning algorithms, and inference-time scaling techniques. - Collaborate across pre-training and post-training teams to deliver step-function gains in model capability. - Contribute to shaping our understanding of how large models learn to reason, follow instructions, and improve through reinforcement learning. ABOUT YOU - Deep understanding of machine learning fundamentals and practical experience with large-scale LLM training. - Strong engineering skills, comfortable diving into complex ML codebases and distributed systems. - Experience improving model behavior through data, reward modeling, or RL techniques. - Evidence of owning ambitious research or engineering agendas that led to measurable model improvements. - Thrive in a fast-paced, high-agency startup environment; bias toward action and clarity of execution. - Able to work fluidly across research and infra boundaries - Strong communication capabilities and comfort working collaboratively - Passionate about advancing the frontier of intelligence. WHAT WE OFFER: We believe that to make intelligence open and accessible to all, you need to start at the foundation. Joining Reflection means building from the ground up as part of a talent-dense team. You will help define our future as a company, and help define the future of open foundational models. We want you to do the most impactful work of your career with the confidence that you and the people you care about most are supported. - Top-tier compensation: Salary and equity structured to recognize and retain our talent globally. - Stock options: Everyone who joins and contributes to Reflection's success gets to share in the upside through stock options. - Health & wellness: Comprehensive medical, dental, vision, and life, with an annual wellness allowance. - Meals: Lunch and dinner are provided in the office daily. - Life & family: 22 weeks paid parental leave for all new birthing and non-birthing parents, including adoptive and surrogate journeys. - Vacation days: Unlimited paid time off in the U.S. and 30 days in the U.K. - Sponsorship support: We sponsor visas to help exceptional talent join our team and support long-term immigration pathways where applicable. - Team building: We have regular off-sites, happy hours, and team celebrations. Export Control Notice: This position may require access to technology or source code subject to the U.S. Export Administration Regulations. Any offer of employment for this role may be conditioned on the Company's ability to provide the candidate with access to such technology or source code in compliance with applicable U.S. export control laws, which may require the Company to seek government authorization.