Sr. Machine Learning Engineer I

HubSpot is an AI-powered customer platform that focuses on helping businesses connect marketing, sales, and service. They are seeking a Senior Machine Learning Engineer to own the models and systems for improving AI agents within their Agent Platform team, specifically working on core ML tasks such as prompt optimization and model fine-tuning.

Responsibilities:

• Design and run experiments to improve agent quality: better tool use, better reasoning, better outputs, using frameworks like DSPy and VLLM
• Build and maintain evaluation infrastructure to measure what's working and catch regressions before customers do
• Optimize LLM inference: latency, cost, model routing, and quality tradeoffs
• Partner with product teams on model selection and performance benchmarking
• Work closely with product engineers and PMs to translate customer quality problems into ML hypotheses and solutions
• Own models end-to-end: from research and experimentation to production deployment

Requirements:

• 5+ years of experience in a dedicated ML Engineer role (not ML-adjacent software engineering)
• Strong Python skills; experience with PyTorch, VLLM, DSPy or similar LLM optimization frameworks
• Hands-on experience working with large language models in production: prompt engineering, fine-tuning, evaluation, inference optimization
• Ability to move from ambiguous problem ('this agent isn't performing well') to experimental design to shipped improvement
• Comfort working with limited supervision in an early-stage product environment