Senior Lead Machine Learning Engineer, Agentic AI

Upwork Inc.’s (Nasdaq: UPWK) family of companies connects businesses with global, AI-enabled talent across every contingent work type including freelance, fractional, and payrolled. This portfolio includes the Upwork Marketplace, which connects businesses with on-demand access to highly skilled talent across the globe, and Lifted, which provides a purpose-built solution for enterprise organizations to source, contract, manage, and pay talent across the full spectrum of contingent work. From Fortune 100 enterprises to entrepreneurs, businesses rely on Upwork Inc. to find and hire expert talent, leverage AI-powered work solutions, and drive business transformation. With access to professionals spanning more than 10,000 skills across AI & machine learning, software development, sales & marketing, customer support, finance & accounting, and more, the Upwork family of companies enables businesses of all sizes to scale, innovate, and transform their workforces for the age of AI and beyond.

Since its founding, Upwork Inc. has facilitated more than $30 billion in total transactions and services as it fulfills its purpose to create opportunity in every era of work. Learn more about the Upwork Marketplace at Upwork.com

We’re seeking a Senior Lead Machine Learning Engineer to architect, ship, and scale the next generation of agentic intelligence across Upwork. You will lead end‑to‑end development of AI agents and the platform that powers them—from LLM training and evaluation to runtime orchestration, safety, and developer APIs. This is a hands‑on, high‑impact role at the intersection of applied research and platform engineering, enabling internal teams and external developers to build reliable, safe, and high‑performing agents on Upwork.

Responsibilities

• Build Agentic Intelligence.  Design and implement multi‑agent systems (planning, tool‑use, memory, debate/critique, reflection) with robust guardrails and recovery strategies.
• Develop protocol‑aware agents and services that interoperate cleanly with developer tooling (e.g., agent frameworks and protocols such as MCP). 
• Own reliability at scale: deterministic execution where needed, idempotency, timeouts/retries, and evaluation‑driven iteration on agent behavior.
• Train, Align, and Evaluate LLMs for Agents.  Lead data strategy and curation for agent tasks; drive SFT, DPO, RLHF/RLAIF, and safety tuning tailored to multi‑tool, multi‑step workflows.
• Stand up evaluation harnesses for functional, task, and longitudinal metrics (success rate, time‑to‑completion, hallucination/escape rates, cost/latency).
• Build policy‑driven guardrails; partner with Legal/Security on data governance and privacy.
• Engineer Agentic Platform Backend Infrastructure.  Architect low‑latency inference, retrieval, and orchestration services (streaming, event‑driven pipelines; scalable queues; caching; batching) with strong SLOs.
• Ship production‑grade services (APIs/SDKs, auth, rate limiting, observability) that make agent features easy to integrate for internal and external developers. 
• Optimize cost/performance via quantization, distillation, model‑routing, and autoscaling; integrate evaluation signals directly into runtime and CI/CD.
• Lead, Partner, and Uplevel the Ecosystem.  Provide technical leadership across research, product, and platform teams; mentor senior ICs; influence roadmaps with clear metrics and trade‑offs.
• Publish internal guidance and exemplar implementations; contribute to technical content, samples, and reference architectures for our agent platform. 
• Define and track KPIs for data/quality/throughput, and drive continuous improvement using experiment results and production telemetry.

What it takes to catch our eye

• Senior level experience applied ML/ML systems, with experience building LLM‑powered products; proven delivery of agentic workflows in production.
• Hands‑on mastery of LLM adaptation (prompting, tool/function calling), data curation, and safety/guardrails.
• Strong software fundamentals (distributed systems, transactions, consistency, resiliency) and experience building high‑throughput microservices/APIs/SDKs.
• Fluency with Python; proficiency in one of Go/Java/Javascript a plus. Experience with container orchestration, messaging/streaming, and observability stacks.
• Experience designing eval suites for agents (task/rubric‑based, offline/online) and closing the loop from evals → training → runtime policy.
• Comfort with cost, latency, and reliability trade‑offs; you use metrics to make crisp decisions under ambiguity.
• Familiarity with agent frameworks and protocols (e.g., MCP; API/SDK design for developer productivity).
• Track record of leading cross‑functional initiatives and mentoring senior engineers; excellent written communication and bias for measurable results.

Come change how the world works.

Upwork is establishing its first international operational hub in Lisbon, Portugal. The new office is expected to be fully operational by Q4 2026.

This position will initially be employed through a partner to ensure a seamless hiring process while we establish the hub. Once the hub is established, there may be opportunities to transition to employment with Upwork depending on business needs and other requirements. While employed by the partner, you’ll work as part of Upwork’s team, with access to our resources, culture, and growth opportunities.

Our partner will offer competitive benefits. When Upwork’s hub is established, we will be excited to offer employment and benefits directly as business needs require. 

Upwork is 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.

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. The Company is committed to conducting an individualized assessment and giving all individuals a fair opportunity to provide relevant information or context before making any final employment decision.

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