Member of Technical Staff - Post-Training

The role

You will build systems that transform pre-trained models into aligned and general agents. You will drive research and engineering initiatives in post-training including data curation and large-scale optimization.

What you will do

• 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.

Required qualifications

• Deep understanding of machine learning fundamentals
• 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
• Comfort working collaboratively
• Passionate about advancing the frontier of intelligence

Benefits

• Top-tier compensation
• Stock options
• Comprehensive medical, dental, vision, and life
• Annual wellness allowance
• Lunch and dinner provided in the office daily
• 22 weeks paid parental leave for all new birthing and non-birthing parents, including adoptive and surrogate journeys
• Unlimited paid time off in the U.S.
• 30 days vacation in the U.K.
• Sponsorship support for visas
• Regular off-sites, happy hours, and team celebrations

Before you apply

• This position may require access to technology or source code subject to the U.S. Export Administration Regulations.
• Any offer of employment may be conditioned on the Company's ability to provide access to technology or source code in compliance with U.S. export control laws.

About the company

Reflection is a research lab making intelligence open and accessible for everyone to use, customize, and build on. They build open models to help shape the future of AI.