Software Engineer, Agent Harness

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.

About the Role

As a Software Engineer on the Agent Harness team at SpaceXAI, you’ll build the core agent behavior and capabilities that power agent experiences across Cursor products. This spans agent orchestration, tools, guardrails, and model behavior tuning—designed as a platform that SpaceXAI engineers can extend and depend on.

Your work will also define the default Cursor agent experience (”Auto”), where users trust us to make the right model choices under real-world constraints.

Example projects include:

• Advancing the agent harness (agent loop, tools, prompts, execution environment, capabilities) used across Cursor products. This would shape and empower experiences like multi-agent coordination.
• Improving the default Cursor agent experience (the “Auto” model setting): making smart model choices based on user needs, model capabilities, and cost appetite.
• Shaping the default Cursor agent’s personality.
• Launching new models on Cursor end-to-end — partnering with foundational model providers and our research team on integration, evaluation, and rollout.

You may be a fit if

• You have built complex agentic products or infrastructure.
• You have strong software engineering fundamentals and enjoy shipping production systems.
• You have taste and strong opinions on model and agent behaviors. You stay up-to-date and informed on emerging research and industry trends.
• You make good calls in the gray area: weighing data, user experience, and product taste when there isn’t a single “right” answer.
• Experience building eval datasets or frameworks to understand and improve the performance of AI systems is a plus.
• Experience building products or tools used by other engineers is a plus.

Applying

If there appears to be a fit, we'll reach to schedule 2-3 short technicals. After, we'll schedule an onsite in our office, where you'll work on a small project, discuss ideas, and meet the team.

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