Research Scientist - LLM

Retell AI is reimagining the call center from first principles using 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, Retell has scaled to $60M ARR with a team of 40 people, up from $5M at the start of 2025.

Retell is a top 50 AI app on the a16z list, ranked #4 on Brex's Fast-Growing Software Vendors of 2025, and one of the top-ranking startups on the Lean AI Leaderboard.

The Opportunity

Retell AI is hiring a Founding Machine Learning Research Engineer to push the boundaries of real-time voice AI. You will 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 at scale.

This is a research role with direct product impact. If you are 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 one of the fastest-growing voice AI companies in the world.

What You'll Do

• •      Explore and develop new techniques across LLMs and audio models to improve reasoning, latency, and conversational quality in real-time systems
• •      Rapidly build and iterate on models and pipelines, turning research ideas into working prototypes; innovate on paradigms, training methods, and inference
• •      Design novel evaluation frameworks, datasets, and metrics to measure performance on complex, real-world voice tasks
• •      Collaborate closely with engineering to translate research insights into deployable systems
• •      Develop methods to incorporate human evaluation into model improvement, especially for subjective conversational quality
• •      Stay at the cutting edge of ML research and bring new ideas into Retell's product and infrastructure

You Should Have

• •      Strong ML research background with experience on advanced problems such as LLM pre-training and post-training, transcription model training, TTS, or multimodal systems, in industry or academia
• •      Deep technical foundation in PyTorch, model architectures, and the math behind modern machine learning
• •      Master's degree in Computer Science, Machine Learning, AI, or a related field; PhD preferred; equivalent research-level engineering experience also considered

Nice to Have

• •      First or co-author publications at top-tier venues such as NeurIPS, ICML, ICLR, ACL, or Interspeech, or notable competition awards
• •      Experience translating research into systems that work in real-world, production environments
• •      Comfort operating in fast-paced environments with high ownership and ambiguity

Compensation and Benefits

Base Salary: $225,000 - $400,000, with three cash-equity balance options offered upfront. Compensation is tied to interview performance, not past salaries.

Benefits include 100% coverage for medical, dental, and vision insurance; $70/day DoorDash credit for meals and snacks; $200/month wellness reimbursement; $300/month commuter reimbursement; $75/month phone reimbursement; and $50/month internet reimbursement.