Sr. Model Engineer, Post-Training & RL

SpaceXAI; Palo Alto (CA); On-site; USD 180,000 - 600,000; Full time

Benefits offered by this job

Equity

Medical Insurance

Vision and Dental

401(k)

Disability Insurance

Life Insurance

Employee Discounts

Job summary

SpaceXSI is seeking a Sr. Model Engineer, Post-Training & RL to tackle post-training and reinforcement learning challenges, including reward modeling and RLHF/DPO to improve reasoning and truthfulness. You will develop capabilities across the Grok stack and applications.

You will work on models with 1B+ parameters, applying production-quality Python, PyTorch, JAX and C++ code to push the boundaries of AI performance and reliability.

Qualifications

• Production-quality Python, PyTorch, JAX, Rust or C++ code experience.
• Experience training large models (1B+ parameters) incl. post-training and RL.

Responsibilities

• Tackle post-training and RL challenges for model alignment and usability.
• Work on reward modeling and preference optimization (RLHF/DPO) to improve reasoning.
• Enhance real-world capabilities of Grok models and related AI stack.

Skills

Python programming

Machine learning

RL fundamentals

Post-training ML

Tools

Python

PyTorch

JAX

Rust

C++

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, POST-TRAINING & RL

You will work on the most critical post-training and reinforcement learning challenges at any given time — including reward modeling, preference optimization (RLHF/DPO), and RL for improving reasoning, truthfulness, and real-world capabilities.

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

• You believe truth-seeking AI is the most important and challenging problem
• You are obsessed about building incredibly useful models through post-training and RL techniques
• You are a power user of AI models and eager to push the boundaries of what's possible with reinforcement learning and alignment methods
• If you previously worked on post-training, RLHF, or trained models used by millions of people it's a big plus, but relevant experience is not required
• You take pride in your work and thrive in meritocratic environments

COMPENSATION AND BENEFITS

$180,000 - $600,000 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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