Member of Technical Staff - Post-Training

Reflection • London, California

5d • Onsite

About The Position

Reflection is a research lab focused on making intelligence open and accessible. We build open models that empower users to control their intelligence and shape the future of AI. This role involves building systems to transform pre-trained models into aligned and general agents. You will drive research and engineering in post-training, including data curation, large-scale optimization, developing data generation pipelines, reward models, reinforcement learning algorithms, and inference-time scaling techniques. Collaboration with pre-training teams is key to improving model capabilities. You will also contribute to understanding how large models learn reasoning, instruction following, and improvement through reinforcement learning.

Requirements

• 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.

Responsibilities

• 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.

Benefits

• 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.

What This Job Offers

• Job Type: Full-time
• Career Level: Senior
• Education Level: No Education Listed