Research Scientist - LLM

About the Role

Retell AI is using first-principles thinking to reimagine the call center with cutting-edge voice AI. Thousands of companies now use Retell's AI voice agents to handle sales, support, and logistics calls that once required large teams of human agents. Backed by Y Combinator, Alt Capital, and other leading investors, we've scaled to $80M in ARR with a team of 50, up from $5M at the start of 2025, and are now valued at over $1.5B. Our vision for 2026 is to build a modern CX platform where entire contact centers are powered by AI. Instead of basic automation that needs constant human tuning, we're creating intelligent AI "workers" that act as frontline agents, QA analysts, and managers, continuously executing, monitoring, and improving every customer interaction. We're growing fast and looking for ambitious builders who want to tackle hard technical problems, move quickly, and have a real impact on one of the fastest-growing voice AI companies in the world. If you're excited about solving open-ended ML problems, experimenting rapidly, and shaping how voice AI systems think and perform, this is a unique opportunity to do so at scale. Let's build the future together.

• No. 1 Best Places to Work in the Bay Area, San Francisco Business Times 2026 https://finance.yahoo.com/technology/ai/articles/voice-ai-startup-Retell Ai-145200025.html
• Top 50 AI Apps, a16z (2025) https://a16z.com/the-ai-application-spending-report-where-startup-dollars-really-go/
• #3 Fastest-Growing Software Company, G2 Best Software Awards 2026 https://company.g2.com/news/g2s-2026-best-software-awards
• Best Agentic AI Software, G2 Best Software Awards 2026 https://www.retellai.com/blog/retell-ai-recognized-as-the-best-agentic-ai-software-by-g2
• #4 Fastest-Growing Software Vendor, Brex Benchmark 2025 https://www.brex.com/journal/brex-benchmark-december-2025
• Enterprise Tech 30 Class of 2026, Nasdaq & Wing VC https://www.nasdaq.com/videos/retell-ai
• Top-Ranked Startup, Lean AI Leaderboard https://leanaileaderboard.com/
• Backed by Y Combinator https://www.ycombinator.com/companies/retell-ai

What You'll Do

Retell AI transforms customer experience with voice AI for enterprises, including customers like CVS/Aetna, American Airlines, Lenovo, and Grab. We have more customer stories than we can tell! This is a research-driven, high-impact role for ML researchers who want to push the boundaries of real-time AI. As a Founding Machine Learning Research Engineer at Retell, you'll focus on advancing model capabilities for human-like voice agents operating in complex, real-world environments. You'll explore new approaches across LLMs and audio models, design novel evaluation methods, and prototype systems that improve reasoning, latency, and conversational quality. Your work will directly influence production systems, bridging cutting-edge research with real-world deployment.

• Research & Experimentation - Explore and develop new techniques across LLMs and audio models to improve reasoning, latency, and conversational quality in real-time systems.
• Model Training - Rapidly build and iterate on models and pipelines, turning research ideas into working prototypes. Innovate on paradigms, training methods, and inference.
• Evaluation & Benchmarking - Design novel evaluation frameworks, datasets, and metrics to measure performance on complex, real-world voice tasks.
• Bridge Research to Production - Collaborate closely with engineering to translate research insights into deployable systems.
• Human Feedback Loops - Develop methods to incorporate human evaluation into model improvement, especially for subjective conversational quality.
• Advance the Frontier - Stay at the cutting edge of ML research and bring new ideas into Retell's product and infrastructure.
• Drive Impact at Scale - Ensure your research directly enhances the performance of production voice AI handling thousands of customer conversations.

Requirements

• Strong ML Research Background - You've worked on advanced ML problems (like LLM pre-training and post-training, transcription model training, TTS, or multimodal systems), either in industry or academia.
• Deep Technical Foundation - Comfortable with PyTorch, model architectures, and the math behind modern machine learning.
• Top Academic Background - Master's degree in CS, ML, AI or related field required; PhD preferred. Equivalent research-level engineering experience also considered.
• Proven Research Output - Track record of publications or contributions at top-tier venues (NeurIPS, ICML, ICLR, ACL, Interspeech, etc.) or recognized competition achievements.
• Experimental Agility - Experience designing and running experiments in open-ended, fast-paced settings.
• Production Pragmatism - Ability to translate research into reliable systems that operate in real-world, high-stakes environments.
• Communication & Collaboration - Strong written and verbal communication to explain complex ideas and work cross-functionally with product and engineering teams.
• Published or Awarded - First/co-author publications at top-tier venues (NeurIPS, ICML, ICLR, ACL, Interspeech, etc.) or notable competition awards are a strong plus.
• Have an Experimental Mindset - You enjoy exploring open-ended problems and iterating quickly on ideas.
• Bridge Theory & Practice - You can translate research into systems that work in real-world environments.
• Are Startup-Ready - You thrive in fast-paced environments with high ownership and ambiguity.
• Are a Collaborative & Clear Communicator - You can explain complex ideas and work cross-functionally to drive alignment and execution.
• Experience with voice AI, speech recognition, or TTS pipelines.
• Contributions to open-source ML libraries or frameworks.

Practical Notes

This role is based in the San Francisco Bay Area. This is a full-time role. We are an equal opportunity employer and all qualified applicants will receive consideration for employment without regard to race, color, religion, gender, gender identity or expression, sexual orientation, national origin, genetics, disability, or status as a veteran. If you require reasonable accommodation for any part of the hiring process, please contact careers@retellai.com. If you need a reasonable accommodation due to a disability or medical condition, please describe the requested accommodation and your current status at careers@retellai.com. Please include "Accommodation Request" in the subject line. If you are applying under the San Francisco Fair Chance Ordinance, you are not required to disclose convictions on your application. If you have additional questions or need assistance, visit https://www.retellai.com/careers or email careers@retellai.com.