Member of Technical Staff – Post‑Training

About the role

Join Reflection, a research lab building open AI models, to develop systems that turn powerful pre‑trained models into aligned, general agents. You will drive research and engineering initiatives across the post‑training pipeline, from data curation to large‑scale optimization.

Key responsibilities

• Build and scale data generation pipelines, reward models, and reinforcement‑learning algorithms.
• Collaborate with pre‑training and post‑training teams to achieve step‑function gains in model capability.
• Contribute to research on how large models learn to reason, follow instructions, and improve through RL.

Required profile

• Deep understanding of machine‑learning fundamentals and hands‑on experience with large‑scale LLM training.
• Strong engineering ability to work in complex ML codebases and distributed systems.
• Proven track record of improving model behavior via data, reward modeling, or RL techniques.
• Ability to thrive in a fast‑paced, high‑agency startup environment.

Required skills

• Machine‑learning fundamentals
• Large‑scale LLM training
• Reinforcement learning (RL) techniques
• Distributed systems engineering

What we offer

• Top‑tier compensation with salary and equity
• Stock options for all contributors
• Comprehensive health, dental, vision, and life coverage plus wellness allowance
• Daily lunch and dinner provided on‑site
• 22 weeks paid parental leave for all new parents
• Unlimited PTO in the U.S. (30 days in the U.K.)
• Visa sponsorship and immigration support
• Regular team off‑sites and celebrations