Lead Machine Learning Engineer/Scientist, Algorithms and Research

Upwork ($UPWK) is the world’s largest work marketplace, connecting businesses with highly skilled professionals worldwide. From entrepreneurs to Fortune 100 enterprises, companies trust Upwork’s platform to access expert talent, leverage AI-powered work solutions, and drive meaningful business outcomes.

Upwork’s AI-powered platform has facilitated over $20 billion in economic opportunity for professionals worldwide. With professionals spanning 10,000+ skills, including AI and machine learning, software development, sales and marketing, customer support, finance and accounting, and more, Upwork empowers businesses of all sizes to scale, innovate, and build agile teams.

We're looking for a Lead Machine Learning Engineer/Scientist to join our Algorithms and Research Team within the ML & AI organization. This team builds foundational models and reinforcement learning (RL) systems that power Upwork’s vertical teams, including Search & Recommendations and Uma, our AI assistant. In this role, you'll focus on designing, developing, and deploying cutting-edge RL systems for reasoning and planning.

You'll contribute to building scalable decision-making and information retrieval systems utilizing structured and unstructured data, and drive innovation through RAG integration combined with advanced RL-based planning  methods.

You’ll partner closely with engineering, research, and trust and safety teams to transition reinforcement learning models from research prototypes into robust, production-ready solutions, enhancing the performance and reliability of Upwork’s evolving platform.

• Design and implement reinforcement learning approaches for reasoning & planning, e.g. leveraging Monte Carlo Tree Search (MCTS) and AlphaGo-like planning algorithms.
• Integrate knowledge graphs and vector databases to enhance context-awareness and decision-making capabilities of RL systems.
• Collaborate with trust and safety stakeholders to investigate explainability and interpretability in reinforcement learning systems, minimizing risks and unintended behaviors.
• Lead cross-functional efforts in advancing RL models from research stages to production, ensuring optimal performance, scalability, and robustness.
• Stay at the forefront of reinforcement learning advancements and champion integration of promising RL innovations into Upwork’s production environment.
• Mentor junior engineers, conduct detailed code reviews, and reinforce best practices in RL and software engineering.
• Deliver high-quality, measurable outcomes aligned with team and organizational strategic goals.

• Proven track record designing and deploying reinforcement learning systems, especially using Monte Carlo Tree Search (MCTS) and policy/value network frameworks.
• Deep understanding and practical experience with vector databases, graph databases, graph neural networks (GNNs), and their applications in RL.
• Familiarity with search, recommendation, and decision-making systems within complex, two-sided marketplaces.
• Passion for developing intelligent, autonomous agent systems utilizing advanced reinforcement learning paradigms and large language models (LLMs).

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 21 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.

We’re proud to offer benefits that go beyond the basics, including comprehensive medical coverage for you and your family, unlimited PTO, a 401(k) plan with matching, 12 weeks of paid parental leave, and an Employee Stock Purchase Plan. Visit our Life at Upwork page to learn more about our values, working principles, and the overall employee experience.

Ready to help shape the future of work? Check out our Careers page and follow us on LinkedIn, Facebook, Instagram, TikTok, and X to learn more about life at Upwork.

Upwork is an Equal Opportunity Employer committed to recruiting and retaining a diverse and inclusive workforce. We do not discriminate based on race, religion, color, national origin, gender (including pregnancy, childbirth, or related medical conditions), sexual orientation, gender identity, gender expression, age, status as a protected veteran, status as an individual with a disability, genetic information, or other legally protected characteristics under federal, state, or local law.

Please note that a criminal background check may be required once a conditional job offer is made. Qualified applicants with arrest or conviction records will be considered in accordance with applicable law, including the California Fair Chance Act and local Fair Chance ordinances.