Sr. Model Engineer, RL Inference
- Salary
- $180,000 - $440,000
- Level
- Senior
Not stated in the posting: work type, visa.
Open. First seen 2 October 2026.
About the role
SpaceXSI's standard text
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 INFERENCE
The RL infrastructure team is looking for an engineer to help with low precision RL training and inference.
RESPONSIBILITIES:
- Design and optimize our inference stack for all shapes of RL workloads at SpaceXSI, from small scale ablations to production training runs
- Analyze, profile and address performance bottlenecks in large scale RL systems
- Work closely with the modeling team to efficiently implement novel RL techniques and algorithms
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 in building, debugging, and optimizing efficiency of large-scale distributed systems
- Experience in LLM inference
- Strong knowledge in quantization and numerics in LLM inference and training
- Experience in developing inference engines, e.g. SGLang, vLLM
- Willingness to dive deep and solve hardcore problems at all levels of the stack
COMPENSATION AND BENEFITS:
$180,000 - $440,000 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.
SpaceXSI's standard text
SpaceXSI is an equal opportunity employer. For details on data processing, view our Recruitment Privacy Notice.
What this role asks for
Particular to this role
LLM · PyTorch
Rare in SpaceXSI's other 163 open postings.
Standard for software engineering roles
Python
Common in software engineering postings at any company.
59% of this description is written for the role. The rest is SpaceXSI's standard text, folded away below.
Compared with SpaceXSI's other open jobs.
The team: Model HIRES STEADILY
This role is one of 11 open in Model. 3 were posted in the last 30 days and the oldest in October: a team that hires all year rather than one being built.
WHAT THE TEAM WORKS WITH, ACROSS ITS POSTINGS
C++ (11 of 11), Python (11 of 11), PyTorch (11 of 11), Rust (11 of 11), LLM (3 of 11), Docker (2 of 11), Kubernetes (2 of 11)
OTHER ROLES ON THIS TEAM
- Sr. Model Engineer, Model Training posted Nov 2
- Sr. Model Engineer, Post-Training & RL posted Nov 2
- Sr. Model Engineer, Mid-training posted Nov 2
- Model Engineer, RL Training Framework posted Jul 14
- Model Engineer, Post-Training & RL posted Apr 29
- Sr. Model Engineer, Multimodal Understanding posted Apr 17
- Model Engineer, Model Training posted Mar 22
- Model Engineer, Voice posted Mar 16
- Model Engineer, Imagine posted Mar 6
- Model Engineer, Mid-training posted Oct 31
From the team and dates on SpaceXSI's own job board.
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