Research Engineer, Applied Research

About the role

Sierra is the leading platform for customer-facing AI agents, working with many of the world's biggest brands — including The GAP, Rocket Mortgage, SoFi, Sutter Health, and SoftBank — to transform how they serve customers and grow their businesses. The company is primarily in-person, based in San Francisco, with growing offices across North America, Europe, and Asia.

Sierra's Applied Research team advances the quality, speed, and cost efficiency of the models powering their agents across a wide range of tasks. Their work spans post-training open-weight models for specialized capabilities and pioneering new approaches to voice AI, turning research breakthroughs into reliable production systems.

The company is guided by core values that define their culture:

• Trust: Building trust with customers through accountability, empathy, quality, and responsiveness; making AI more accessible, safe, and useful; showing up for each other professionally and personally.
• Customer Obsession: Deeply understanding customers' business goals and relentlessly focusing on driving outcomes, not just technical milestones. Everyone knows and spends time with customers; when a customer has an issue, they drop everything and fix it.
• Craftsmanship: Getting the details right, from words on the page to system architecture. Having good taste, taking time to fix what isn't right, taking pride in products, and continuously self-reflecting to improve.
• Intensity: Playing to win, caring about the product being the best, fixing it when it isn't, and talking openly about failures without blame to succeed next time.
• Family: Balancing intensity with balance, modeling it in actions and processes. Striving to be the best technology company for parents, supporting and respecting each other, and celebrating personal and professional achievements.

Co-founders Bret Taylor (Board Chair of OpenAI, former co-CEO of Salesforce, CTO of Facebook, early Google PM and co-creator of Google Maps) and Clay Bavor (18 years at Google, most recently leading Google Labs, previously started and led Google's AR/VR effort Project Starline and Google Lens, led product and design for Google Workspace).

Responsibilities

• Tackle unsolved applied AI and ML problems, pushing the boundaries of post-training, voice AI, and long-horizon task execution to build agents that can reason, adapt, and reliably carry out complex tasks for customers.
• Determine when to build specialized models and when to use externally provided frontier intelligence, balancing quality, speed, and cost to deliver customer value.
• Turn ambiguous product and customer problems into well-framed machine learning problems.
• Develop, fine-tune, evaluate, and deploy models that improve Sierra's customer-facing AI agents.
• Advance post-training work, from supervised fine-tuning toward reinforcement learning and long-horizon optimization.
• Build rigorous evaluations that connect model performance to real-world agent quality.
• Work with large-scale, proprietary datasets spanning text and audio interactions.
• Collaborate across Sierra while taking ideas from experimentation through production deployment and customer impact.

Requirements

• Strong experience building and deploying production machine learning and AI systems (backgrounds across applied ML welcome, including search, ranking, recommendations, advertising, language, and speech).
• Excellent judgment in framing product problems as ML tasks and selecting the simplest, most effective approach.
• Experience working deeply with data, experimentation, evaluation, and model iteration.
• A practical, evidence-driven approach to ML, with strong judgment around when a problem calls for modeling and when a simpler solution will deliver the best outcome.
• The ability to operate with high agency and work across the stack when needed to deliver an outcome.
• Alignment with Sierra's values, including Craftsmanship, Customer Obsession, and Competitive Intensity.
• A degree in computer science, machine learning, or a related field, or equivalent professional experience.

Qualifications

• Experience with supervised fine-tuning or reinforcement learning.
• Experience in search, ranking, recommendations, or advertising systems.
• Experience training and deploying language, speech, or multimodal models.
• Experience designing model evaluations tied to real-world product outcomes.
• Experience working with large-scale consumer datasets or high-volume ML products.
• Contributions to applied ML research or benchmarks.

Benefits

Benefits for full-time employees (further detailed in Sierra's policies, may vary by region, subject to change):

• Flexible (unlimited) paid time off
• Medical, dental, and vision benefits for you and your family
• Life insurance and disability benefits
• Retirement plan dependent on country of employment
• Parental leave
• Fertility and family building benefits through Carrot
• Lunch, as well as delicious snacks and coffee
• Discretionary benefit stipend
• Free alphorn lessons

Eligible full-time employees can participate in Sierra's equity plans subject to the terms of the applicable plans and policies.