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Member of Technical Staff - Post-Training

Reflection· Research
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San Francisco, CA, London, New York, NYFull-timePosted 11mo ago

About the role

Role focused on transforming pre-trained models into aligned, general agents, advancing post-training research and engineering from data curation to large-scale optimization, and collaborating across pre-training and post-training teams to improve model capability.

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.

Qualifications

  • 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.

Skills

Required:Machine learning fundamentalsEngineering in ML codebases and distributed systemsData, reward modeling, or RL techniquesResearch / engineering agenda ownershipCross-functional collaboration

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: Regular off-sites, happy hours, and team celebrations.
Last updated Oct 1, 2026. Interested? Apply on the company site.

About Reflection

Building frontier open intelligence

Building frontier open intelligence.

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