Sr. Model Engineer, RL Training Framework

X AI; Palo Alto (CA); On-site; USD 180,000 - 400,000; Full time

Benefits offered by this job

Equity

Medical, vision, dental

401(k) retirement plan

Disability insurance

Life insurance

Job summary

SpaceXSI in Palo Alto is seeking a Sr. Model Engineer to join our RL Training Framework team. You will design and implement the systems backing RL workloads, from small-scale ablations to production training runs, in a high-performance stack.

You will profile, debug, and optimize end-to-end training performance, and improve scalability and observability of the RL stack, enabling 1B+ parameter models and beyond. The role offers a competitive package with equity and comprehensive benefits.

Qualifications

• Experience writing production-quality code in Python, PyTorch, JAX, Rust or C++.
• Experience training large models (1B+ parameters) including RL training.
• Experience building, debugging, and optimizing large-scale distributed systems.

Responsibilities

• Design and implement the systems backing all RL workloads at SpaceXSI, from small scale ablations to production training runs.
• Profile, debug, and optimize end-to-end training performance.
• Improve scalability and observability of the RL stack.

Skills

Python

PyTorch

JAX

Rust

C++

Distributed systems

LLM training

RL techniques

Job description

SpaceX was founded under the belief that a future where humanity is out exploring the stars is fundamentally more exciting than one where we are not. Today, SpaceX is actively developing the technologies to make this possible, with the ultimate goal of making life multiplanetary and expanding consciousness to the stars.

SpaceXSI is building Super Intelligence to help humanity understand the universe. Our teams are building the full Super Intelligence stack: from our Colossus supercomputers, to Grok models, to our suite of applications, including Grok Bot, Grok Build, Grok Imagine, Grok Voice, and X. We're creating a powerful flywheel where more compute trains better models, better models power more useful products, and what we learn from people using those products shapes what we build next.

SR. MODEL ENGINEER, RL TRAINING FRAMEWORK

The RL infrastructure team is looking for an engineer to help develop our RL training framework.

RESPONSIBILITIES:

• Design and implement the systems backing all RL workloads at SpaceXSI, from small scale ablations to production training runs
• Profile, debug, and optimize end-to-end training performance
• Improve scalability and observability of the RL stack

BASIC QUALIFICATIONS:

• Experience writing production-quality code in Python, PyTorch, JAX, Rust, or C++
• Experience training large models (e.g., pre-training, post-training, fine-tuning, or RL training of neural networks with 1B+ parameters)

PREFERRED SKILLS AND EXPERIENCE:

• Experience building, debugging, and optimizing efficiency of large-scale distributed systems
• Experience with large scale LLM training infrastructure
• Experience with RL numerics
• Strong knowledge of reinforcement learning techniques
• Comfortable diving into unfamiliar areas and solving problems at all levels of the stack

COMPENSATION AND BENEFITS:

$180,000 - $400,000 USD

• Base salary is just one part of our total rewards package at SpaceXSI, which also includes equity, comprehensive medical, vision, and dental coverage, access to a 401(k) retirement plan, short & long-term disability insurance, life insurance, and various other discounts and perks.

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