Model Engineer - RL & Frontier-Scale AI

Cursor; Palo Alto (CA); On-site; USD 160,000 - 250,000; Full time

Job summary

SpaceXSI is seeking a Model Engineer to drive RL research and scalable training for frontier-scale models. You will own end-to-end research problems, design rigorous experiments, and collaborate with engineers to move small results into large-scale runs.

The role requires onsite work at the Palo Alto office and a strong background in ML, RL, and Python-based systems. SpaceXSI offers a competitive package with equity and comprehensive benefits.

Qualifications

• Production-quality coding experience in Python, PyTorch, JAX, Rust or C++.
• Ability to design and run rigorous experiments and own research direction end to end.
• Hands-on experience training large models and RL.
• Experience with RL algorithms for language models, scaling laws, or building RL environments and evals.
• Experience with distributed training at scale and debugging problems that only show up at scale.
• MS or PhD in CS, ML, math, physics or related field, or equivalent research experience.

Responsibilities

• Design and run rigorous experiments that turn research ideas into measurable gains in model capability.
• Improve data recipes through data quality, deduplication, and mixture experiments.
• Define what makes RL data and rewards good, including grader design and preventing reward hacking.
• Advance training science, from architecture and scaling experiments to post-training recipes for coding and computer-use agents.
• Build evals and targeted tasks that expose model weaknesses and guide where the team invests next.
• Partner with engineers to take promising results from small experiments to frontier-scale training runs.

Skills

Production-quality coding

Experimental design

Research direction

RL for language models

Distributed training

Machine learning fundamentals

Software engineering

Python

PyTorch

JAX

Rust

C++

Education

MS or PhD in CS, ML, math, physics or related field

Tools

Python

PyTorch

JAX

Rust

C++

Job description

SpaceXSI is seeking a Model Engineer to drive RL research and scalable training for frontier-scale models. You will own end-to-end research problems, design rigorous experiments, and collaborate with engineers to move small results into large-scale runs.

The role requires onsite work at the Palo Alto office and a strong background in ML, RL, and Python-based systems. SpaceXSI offers a competitive package with equity and comprehensive benefits.