Software Engineer - Network (C++)

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 understand the universe and help expand humanity’s knowledge and capabilities. We work across the full Super Intelligence stack: compute (Colossus supercomputers), models (Grok), and applications (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.

ABOUT THE ROLE:

At SpaceXSI, we design, build, and operate Colossus from the ground up. This includes the massive GPU clusters, high-speed interconnect fabric, and the software that makes it all work at unprecedented scale. Colossus powers Grok and our frontier AI models with a custom, high-performance datacenter network that delivers ultra-low latency and massive bandwidth across hundreds of thousands of GPUs.

As a Software Engineer on the Colossus Networking team, you will develop the core networking software that maximizes the performance and reliability of our datacenter fabric. Your work will directly impact training efficiency, model convergence, and the speed at which we can push the frontier of AI.

Our engineers own the full lifecycle of their software — from design and implementation to deployment, monitoring, and iteration based on real-world performance at scale. You will solve hard problems in distributed systems, high-performance networking, and real-time control of one of the largest AI supercomputers on Earth.

RESPONSIBILITIES:

• Develop routing and traffic-engineering algorithms for the Colossus high-performance datacenter network.
• Develop highly reliable, real-time software designed to run on the switches that form the backbone of our low-latency, high-bandwidth AI training fabric.
• Participate in and lead architecture, design, and code reviews.
• Develop prototypes and run experiments to validate key design decisions at both small and full-cluster scale.
• Build tools for software development, deployment, data analysis, visualization, and testing across virtualized environments, hardware-in-the-loop setups, and live production clusters.
• Deploy reliable software updates through continuous integration and release systems with rigorous testing and monitoring.
• BASIC QUALIFICATIONS: Bachelor’s degree in computer science, engineering, math, or a related technical discipline; OR 2+ years of professional software development experience in lieu of a degree.
• Strong development experience in C or C++.
• PREFERRED SKILLS AND EXPERIENCE: Strong professional experience writing high-performance C/C++ in production environments.
• Experience developing, debugging, and deploying software that runs at scale in real-world systems.
• Deep knowledge of networking protocols (UDP, TCP/IP, RDMA, etc.), distributed systems, and large-scale datacenter fabrics.
• Background in real-time systems, high-performance computing, low-latency networking, or resource-constrained environments.
• Creative problem-solving ability with exceptional analytical skills and strong engineering fundamentals.
• Excellent written and verbal communication skills.
• Ability to thrive in a fast-paced, dynamic environment with evolving requirements.
• Experience with security considerations in large-scale distributed systems.