Model Engineer, Multimodal Understanding

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

Job summary

SpaceXSI is building a multimodal AI stack and seeks a Model Engineer focused on multimodal understanding to push toward superhuman capabilities. You will design distributed systems for pre-training, post-training, and inference, handling data, tokenization, and real-time interactions at web/petabyte scales.

You will collaborate with cross-functional teams to advance world modeling, tool use, and interactive human-AI collaboration, delivering frontier capabilities and high-throughput pipelines.

Qualifications

• Production-quality code in Python, PyTorch, JAX, Rust or C++.
• Expert-level Python proficiency with at least one of JAX / PyTorch / XLA.
• Proven track record building or optimizing large-scale distributed ML systems.
• Strong data pipelines at scale: curation, filtering, generation, quality studies.
• Fundamentals in evaluation design, benchmarks, reward modeling, or RL.
• Experience with multimodal LLMs, tokenizers, or scaling laws.
• Hands-on work with orchestration tools such as Spark, Ray, or Kubernetes.
• Background in full-stack tooling for real-time research demos/apps.

Responsibilities

• Design, build, and optimize large-scale distributed systems for multimodal pre-training/post-training/inference.
• Develop high-throughput data acquisition, preprocessing, filtering, generation, decoding, and loading pipelines.
• Advance multimodal capabilities across modalities and real-time video processing.
• Drive data quality studies and scalable pipelines for trillion-parameter models.
• Create evaluation frameworks, benchmarks, reward models, and metrics for real-world use.
• Innovate on algorithms, modeling, co-design, and scaling paradigms for state-of-the-art performance.
• Build research tooling, demos, and end-to-end product experiences for rapid iteration.
• Collaborate with cross-functional teams to enable reasoning and tool use in real time.

Skills

Python

PyTorch

JAX

Rust

C++

Distributed ML

Data pipelines

Evaluation design

RL techniques

Multimodal AI

Tools

Spark

Ray

Kubernetes

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.

MODEL ENGINEER, MULTIMODAL UNDERSTANDING

You will join the multimodal team to push toward superhuman multimodal intelligence. Advance understanding and generation across modalities-image, video, audio, and text-spanning the full stack: data curation/acquisition, tokenizer training, large-scale pre-training, post-training/alignment, infrastructure/scaling, evaluation, tooling/demos, and end-to-end product experiences.

Collaborate cross-functionally with pre-training, post-training, reasoning, data, applied, and product teams to deliver frontier capabilities in multimodal reasoning, world modeling, tool use, agentic behaviors, and interactive human-AI collaboration. Contribute to building models that can see, hear, reason about, and interact with the world in real time at unprecedented levels.

RESPONSIBILITIES:

• Design, build, and optimize large-scale distributed systems for multimodal pre-training, post-training, inference, data processing, and tokenization at web/petabyte scale
• Develop high-throughput pipelines for data acquisition, preprocessing, filtering, generation, decoding, loading, crawling, visualization, and management (images, videos, audio + text)
• Advance multimodal capabilities including spatial-temporal compression, cross-modal alignment, world modeling, reasoning, emergent abilities, audio/image/video understanding & generation, real-time video processing, and noisy data handling
• Drive data quality and studies: curation (human/synthetic), filtering techniques, analysis, and scalable pipelines to support trillion-parameter models
• Create evaluation frameworks, internal benchmarks, reward models, and metrics that capture real-world usage, failure modes, interactive dynamics, and human-AI synergy
• Innovate on algorithms, modeling approaches, hardware/software/algorithm co-design, and scaling paradigms for state-of-the-art performance
• Build research tooling, user-friendly interfaces, prototypes/demos, full-stack applications, and enable rapid iteration based on feedback
• Work across the stack (pre-training → SFT/RL/post-training) to enable reasoning, tool calling, agentic behaviors, orchestration, and seamless real-time interactions

BASIC QUALIFICATIONS:

• Experience writing production-quality code in Python, PyTorch, JAX, Rust, or C++

PREFERRED SKILLS AND EXPERIENCE:

• Expert-level proficiency in Python (core language), with strong experience in at least one of: JAX / PyTorch / XLA
• Proven track record building or optimizing large-scale distributed ML systems (training/inference optimization, GPU utilization, multi-GPU/TPU setups, hardware co-design)
• Deep experience designing and running data pipelines at scale: curation, filtering, generation, quality studies, especially for noisy/real-world multimodal data
• Strong fundamentals in evaluation design, benchmarks, reward modeling, or RL techniques (particularly for interactive/agentic behaviors)
• Proactive self-starter who thrives in high-intensity environments and is passionate about pushing multimodal AI frontiers
• Willingness to own end-to-end initiatives and do whatever it takes to deliver breakthrough user experiences
• Experience leading major improvements in model capabilities through better data, modeling, algorithms, or scaling
• Familiarity with state-of-the-art in multimodal LLMs, scaling laws, tokenizers, compression techniques, reasoning, or agentic systems
• Proficiency in Rust and/or C++ for performance-critical components
• Hands-on work with large-scale orchestration tools such as Spark, Ray, or Kubernetes
• Background building full-stack tooling: performant interfaces, real-time research demos/apps, or end-to-end product ownership
• Passion for end-to-end user experience in interactive, real-time multimodal AI systems

COMPENSATION AND BENEFITS:

• $160,000 - $250,000 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 is an equal opportunity employer. For details on data processing, view our Recruitme