Principal Machine Learning Engineer

HubSpot is seeking a Principal Machine Learning Engineer in Cambridge, MA (onsite) to build foundational AI infrastructure that enables agentic product experiences. The role will focus on core platform capabilities such as agent runtime, evaluation systems, quality measurement, and model optimization to improve evaluation quality, product experience, and scalability across the organization.

Key Responsibilities

• Build infrastructure spanning agent runtime, evaluation, quality measurement, and model optimization.
• Create tooling that helps teams interpret evaluation strengths, identify missing coverage, and detect user question types the system is not yet prepared to handle.
• Design signal pipelines that surface user frustration, agent failure states, and quality issues before they materialize as CSAT declines.
• Help define a HubSpot-specific AI benchmark to evaluate model performance on real HubSpot workloads.
• Develop 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.

Required Qualifications

• Deep experience with production ML, LLM, or AI infrastructure.
• Experience building large-scale systems where reliability, latency, quality, and cost are all important considerations.
• Ability to think in platforms rather than one-off implementations.
• Capability to collaborate across infrastructure, product, backend, and ML teams.
• Experience in one or more of the following areas: evaluation frameworks, model serving, fine-tuning, signal extraction, experimentation, feedback loops, or model optimization.
• Interest in ambiguous, foundational problems where many aspects still need to be defined.
• Ability to influence senior engineers and leaders through technical credibility and clear judgment.

About the Team

HubSpot is building foundational AI infrastructure that powers its next generation of agentic product experiences. This team owns Breeze Engine, the platform behind Breeze Assistant and other AI-powered product experiences, and Aviator, HubSpot’s internal framework for building and running agents. This is a high-scope infrastructure role focused on leverage across the company, rather than a feature-team assignment.

Location

Cambridge, MA (onsite)

Compensation

USD 285,800 - 457,300 per year

Work Arrangement and In-Person Requirements

• Remote employees and office-based employees are required to attend a regional HubSpot office for in-person onboarding if they join the Engineering team.
• If you join HubSpot’s broader Product team, you will attend other in-person events, including a Product Group Summit and additional gatherings.
• If you require an accommodation due to travel limitations or other reasons, you should inform your recruiter during the hiring process so alternative arrangements can be discussed.