Senior Product Engineer

About Blacksmith We started by building infrastructure to run CI workloads really fast. Our first product helps companies run GitHub Actions substantially faster and cheaper by owning and operating our own global fleet of bare-metal machines rather than renting generic cloud VMs. Today, we orchestrate tens of millions of Firecracker VMs each week, running CI for 10,000+ companies and tens of millions in ARR. We’ve grown 20x so far in 2026. We operate thousands of bare-metal machines across multiple regions, regularly schedule 300k+ vCPUs concurrently, and run a petabyte-scale Ceph cluster that we manage ourselves. We’ve raised $125M from Seed to Series C, led by Sequoia, Google Ventures (GV) & Peak XV Partners, and we’re intentionally building a small, but exceptional team. Blacksmith was founded by a team with deep systems and scaling experience, including building search/ads infrastructure at Faire, and operating large distributed systems at Cockroach Labs. Our GTM is led by Jon Boyer, formerly Head of Sales at Zapier. We're now extending the same CI infrastructure into a broader platform: running agent sandboxes at scale and building our own background coding agent on top of it. What you could work on Build and evolve Codesmith, our background coding agent — designing the workflows, UI, and infrastructure that let engineers delegate coding tasks to AI and ship faster Create tools that help engineers and AI agents debug flaky CI jobs: surfacing patterns in test failures, correlating logs with infrastructure signals, and making root cause analysis fast and intuitive Work closely with design to ship polished, high-performance product surfaces across our analytics and observability platform, where engineers go to understand their CI systems Prototype and iterate rapidly on AI-powered features — from natural language interfaces to automated fix generation — and own the full stack from prompt design to backend service to UI Contribute to the architecture of the agent platform: how we run sandboxed workspaces, and orchestrate agent sessions You are a good fit if you Have strong CS fundamentals and a deep understanding of React and modern frontend development. Can work closely with design to build polished, high-performance UIs — and aren’t afraid to go deep on browser performance, rendering bottlenecks, or complex component architecture. Have 5+ years of software development experience. Enjoy working in person 5 days a week in NYC. Enjoy working at a very early-stage startup and are comfortable with ambiguity. Bonus You’ve dabbled in your own side hustles or start-up projects. You’re comfortable creating new processes and iterating on them quickly. Compensation and benefits Medical, Vision, and Dental insurance. Competitive base + equity. 401K match. Unlimited PTO. Annual offsite. Early-exercise stock options 12 weeks fully paid parental leave (US)