Principal Machine Learning Engineer

HubSpot • Cambridge, MA

6d

About The Position

HubSpot is building the foundational AI infrastructure that powers our next generation of agentic product experiences. We’re looking for a Principal Machine Learning Engineer to help shape the base layer that product teams build on: agent runtime, evaluation systems, quality signals, model optimization, fine-tuning, and model routing. This team owns Breeze Engine, the platform behind Breeze Assistant and other AI-powered product experiences, as well as Aviator, HubSpot’s internal framework for building and running agents. This is not a feature-team role; it is a high-scope infrastructure role focused on building systems that create leverage across the company.

Requirements

• Deep experience with production ML, LLM, or AI infrastructure.
• Built systems at scale where reliability, latency, quality, and cost matter.
• Thinks in platforms, not one-off solutions.
• Can work across infrastructure, product, backend, and ML teams.
• Experience with areas like eval frameworks, model serving, fine-tuning, signal extraction, experimentation, feedback loops, or model optimization.
• Is excited by ambiguous, foundational problems where many of the answers still need to be invented.
• Can influence senior engineers and leaders through technical credibility and clear judgment.

Responsibilities

• Build infrastructure for agent runtime, evaluation, quality measurement, and model optimization.
• Create tooling that helps teams understand where their evals are strong, where coverage is missing, and where users are asking questions the system is not yet prepared to handle.
• Design signal pipelines that surface user frustration, agent failure states, and quality issues before they show up as CSAT drops.
• Help define a HubSpot-specific AI benchmark for evaluating model performance on real HubSpot workloads.
• Build systems to evaluate new models across agents, improving product quality, reducing cost, and supporting future model routing.
• Make fine-tuning and task-specific optimization more repeatable for HubSpot’s AI use cases.

What This Job Offers

• Job Type: Full-time
• Career Level: Senior
• Education Level: No Education Listed