We’re looking for a Lead Machine Learning Engineer / Scientist to join our Algorithms and Research team within the ML & AI organization. In this role, you will help shape the reinforcement learning systems that power high-impact experiences across Upwork, including Search & Recommendations and Uma, our AI assistant. You will design and scale advanced reasoning, planning, and retrieval systems that connect research innovation to production outcomes. This is a hands‑on, high‑ownership role for someone excited to push the frontier of RL, autonomous agents, and applied machine learning on a fast‑evolving platform.

This role will require 3 days in office once we have an office open.

Responsibilities:

- Design and advance reinforcement learning systems for reasoning and planning, including approaches inspired by Monte Carlo Tree Search, policy and value networks, and modern agentic decision‑making methods.
- Build scalable retrieval and decisioning architectures that combine structured and unstructured data, including vector search, knowledge graphs, and retrieval‑augmented generation workflows.
- Lead cross‑functional efforts to move ML and RL models from research prototypes into reliable production systems with strong performance, robustness, and observability.
- Partner closely with engineering, research, and Trust & Safety teams to improve explainability, interpretability, and risk mitigation across reinforcement learning and agent‑based systems.
- Evaluate emerging techniques in reinforcement learning, planning, and LLM‑enabled systems, and translate promising innovations into practical applications for Upwork’s platform.




- Mentor engineers and scientists through technical leadership, thoughtful code reviews, and strong software engineering practices that raise quality across the team.
- Deliver high‑impact outcomes aligned with organizational goals, while helping create clarity, structure, and momentum across complex cross‑functional initiatives.

What It Takes to Catch Our Eye:

- Proven experience designing, training, and deploying reinforcement learning systems in production, with deep familiarity in planning methods such as Monte Carlo Tree Search and policy or value‑based approaches.
- Strong expertise in machine learning systems that use vector databases, graph databases, knowledge graphs, or graph neural networks to improve reasoning and decision quality.
- Track record of leading technically complex initiatives across research and engineering partners, with the judgment to balance experimentation, scalability, and production reliability.
- Experience applying AI tools and iterative prompt or workflow strategies to accelerate model development, analysis, debugging, or experimentation while maintaining robust technical rigor.
- Passion for building intelligent agent systems that combine reinforcement learning, large language models, and retrieval techniques to solve meaningful product and platform challenges.

We are committed to building a diverse, inclusive, and equitable workforce. Employment decisions are made without regard to race, color, religion, gender, sexual orientation, gender identity, national origin, disability, or any other status protected by applicable law.

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📌 Lead Machine Learning Engineer / Applied Scientist (Toronto)
🏢 HR Tech Job
📍 Toronto