Senior C# Full-Stack Engineer — AI Data & Infrastructure

Seattle

**About The Role** What if your C# expertise could directly shape the infrastructure powering the next generation of AI? We're looking for a Senior C# Full-Stack Engineer to build and optimize the data pipelines, annotation tooling, and evaluation systems that leading AI labs depend on --- working on real production systems with genuine, measurable impact. This is a fully remote contract role with flexible hours. If you're a sharp systems thinker who loves solving hard infrastructure problems, this is the kind of work that will actually push you. * Organization: Alignerr * Type: Hourly Contract * Location: Remote * Commitment: 20--40 hours/week **What You'll Do** * Design, build, and optimize high-performance C# systems supporting large-scale AI data pipelines and evaluation workflows * Develop full-stack tooling and backend services for data annotation, validation, and quality control at scale * Improve reliability, performance, and safety across existing C# codebases --- hunt down bottlenecks and ship scalable fixes * Collaborate directly with data, research, and engineering teams to support model training and evaluation workflows * Identify edge cases and systemic issues in data and system behavior and implement robust solutions * Participate in synchronous design reviews to iterate on architecture and implementation decisions **Who You Are** * Full-stack developer with a strong systems programming background and 3--5+ years of professional C# experience * Confident writing production-quality code with a focus on modern C# standards and best practices * Deep understanding of performance optimization, concurrency (threading, atomics), and memory safety * Clear, precise written and verbal communicator --- you can articulate technical decisions without hand-waving * Self-directed and reliable when working remotely with minimal supervision * Native or fluent English speaker * Able to commit 20--40 hours per week on a consistent basis **Nice to Have** * Prior experience with data annotation, data quality pipelines, or AI evaluation systems * Familiarity with AI/ML workflows, model training, or benchmarking infrastructure * Experience with distributed systems or developer tooling * Background working in fast-moving research or applied ML environments **Why Join Us** * Work directly with leading AI labs on cutting-edge production systems --- not toy projects * Fully remote and flexible --- structure your work around your life * Freelance autonomy with the focus and momentum of high-impact engineering work * Collaborate with world-class data, research, and engineering teams pushing the frontier of AI * Potential for ongoing work and contract extension as projects scale