Senior Model Engineer Post-Training and Reinforcement Learning
SpaceXAI builds frontier AI models and products including the Grok conversational assistant and a multimodal developer API.
Funding history
About SpaceXAI
SpaceXAI is a US-based AI company focused on accelerating scientific discovery and understanding the universe through reasoning, voice, image, video, and generative AI systems. Formerly xAI, it was acquired by SpaceX effective February 2, 2026, while continuing to operate the x.ai site and services.
Skills
Candidate Availability
Required and preferred rules are kept separate and reflect the wording in the original posting.
About the Role
You will design rigorous experiments, improve model recipes through data-quality and mixture experiments, define effective reinforcement-learning data and rewards, advance training science, build targeted evaluations, and help scale successful experiments into frontier training runs.
Requirements
- Production-quality programming in Python, PyTorch, JAX, Rust, or C++
- Experience training large models, including pre-training, post-training, fine-tuning, or reinforcement learning training of neural networks with more than 1 billion parameters
- Post-training
- Reinforcement learning
- Reward modeling
- Preference optimization
- RLHF
- DPO
- Model evaluation
- Alignment
Responsibilities
- Design and run rigorous experiments that produce measurable gains in model capability
- Improve model recipes through data quality, deduplication, and mixture experiments
- Define effective reinforcement learning data and rewards, including grader design and reward-hacking prevention
- Advance training science through architecture, scaling, and post-training experiments
- Build evaluations and targeted tasks that expose model weaknesses
- Partner with engineers to scale promising results from small experiments to frontier training runs
Benefits
- Equity
- Comprehensive medical coverage
- Vision coverage
- Dental coverage
- 401(k) retirement plan
- Short-term disability insurance
- Long-term disability insurance
- Life insurance
- Discounts and perks
