Senior Lead Machine Learning Engineer - San Diego California

Company: Upwork
Location: San Diego, California
Posted On: 03/11/2026

Upwork ($UPWK) is the world’s human and AI-powered work marketplace that connects businesses with highly skilled, AI-enabled independent talent from across the globe. From entrepreneurs to Fortune 100 enterprises, companies rely on Upwork’s trusted platform and its mindful AI companion, Uma, to find and hire expert talent, leverage AI-powered work solutions, and drive business transformation. With on-demand access to professionals spanning more than 10,000 skills across AI & machine learning, software development, sales & marketing, customer support, finance & accounting, and more, Upwork enables businesses of all sizes to scale, innovate, and build agile teams for the age of AI and beyond. Were looking for a Sr Lead MLE/Applied Scientist to define how success is measured for AI agents performing real-world tasks. This role is at the forefront of building trust and quality into agentic systems by crafting rigorous, reproducible evaluation frameworks that shape what we ship. You’ll work cross-functionally to evaluate humanAI collaboration, assess outcomes beyond accuracy metrics, and uncover what’s truly working for freelancers and clients. Join us in revolutionizing agent evaluation and making a measurable impact on AI systems that power the future of work. Responsibilities • Design and implement comprehensive evaluation frameworks that reflect real-world task success for agentic systems, with a focus on humanAI collaboration outcomes • Build benchmarking pipelines that capture nuanced success indicators including trust calibration, intervention frequency, and agent handoff quality • Lead development of observability tools and instrumentation for analyzing agent behavior in production • Translate complex qualitative and quantitative signals into actionable insights that inform model iteration and product prioritization • Collaborate with researchers, engineers, and product teams to align evaluation methodologies with business and user goals • Own benchmarking infrastructure that enables reproducible, scalable evaluation across AI initiatives • Champion rigorous experimental design and statistical analysis across teams to ensure consistent and meaningful measurement standards What it takes to catch our eye • Proven experience designing evaluation systems for agentic or LLM-based AI, ideally in complex, interactive or open-ended environments • Deep expertise in statistical experimentation, benchmark creation, and human-AI interaction assessment • Fluency in building data pipelines and tooling using Python, SQL, and distributed data processing frameworks • Demonstrated ability to influence product and model roadmaps through evaluation insights and performance measurement • Adaptive-level proficiency in integrating AI tools into technical workflows for analysis, experimentation, and observability refinement Come change how the world works. At Upwork, you’ll shape the future of work for a global, remote-first workforce, creating economic opportunities for professionals worldwide. While we have a physical office in Palo Alto, we currently hire full-time employees in 34 U.S. states, making it easier than ever to join our mission from wherever you call home. Our culture is built on trust, risk-taking, customer focus, and excellence, all in service of our core mission: to create economic opportunities so people have better lives. We embrace authenticity and inclusion, encouraging everyone to bring their whole selves to work. Personal and professional growth is a priority here, supported through development programs, mentorship, and our Upwork Belonging Communities. More...

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