Retell AI

A leading Voice AI startup is seeking a Senior Software Engineer - Backend to shape the core systems for millions of AI-driven conversations. This role involves working with real-time audio and global telephony, leading complex projects, and collaborating across teams. Preferred candidates should have over two years of backend development experience, particularly in scalable systems. The compensation package ranges from $215,000 to $290,000 annually, along with various benefits including medical coverage and wellness reimbursements.

Get AI-powered advice on this job and more exclusive features. This range is provided by Retell AI. Your actual pay will be based on your skills and experience - talk with your recruiter to learn more. Base pay range $215,000.00/yr - $290,000.00/yr Additional compensation types Annual Bonus and Stock options Direct message the job poster from Retell AI AI Building the most human-like AI for automating phone calls for businesses. About Retell AI At Retell AI, we're not just automating calls-we're transforming how the world communicates. Our AI voice agents are reshaping sales, support, and customer engagement for leading brands. Backed by Alt Capital, Y Combinator, and top-tier investors, we've raised $4.7M in seed funding and hit $14M ARR with just 12 people. We're one of the fastest-growing Voice AI startups and we're on a mission to become the standard for voice automation at scale. We're also one of the top ranking startups at About the Role As a Founding Senior Backend Engineer, you'll shape the core systems powering millions of AI-driven conversations. You'll tackle real-time audio, global telephony, and developer tooling, working across the stack with the founding team. This high-impact role offers rapid feedback loops, customer collaboration, and the chance to define a category-leading product. Key Responsibilities Build foundational architecture for Retell's platform, such as prompt orchestration, testing frameworks, observability dashboards, and telephony integrations. Design scalable backend systems and DevOps workflows for reliable performance across millions of calls. Lead complex projects from architecture to production, driving delivery and monitoring. Collaborate with product and design teams to create intuitive APIs and interfaces for quick customer onboarding. Support customer onboarding, troubleshoot issues, and turn feedback into product improvements. Have 2+ years of backend development experience with a degree in CS, CE, or EE. Take ownership like a founder, with a passion for impactful software. Thrive in fast-paced, ambiguous environments, solving new problems with curiosity. Communicate clearly, collaborate across teams, and drive momentum. Have startup experience or grit to adapt, with bonus points for cloud infra/DevOps knowledge. Job Type : Full-time, 70 hr/week (50 hr/week onsite with flexible hours + 20 hr/week work from home) Cash: 215k - 290k Equity : 0.4 - 0.6% Location : Redwood City, CA, US US Visas : Sponsors Visa & Green Card Other Benefits Unlimited breakfast, lunch, dinner, and snacks Gym and daily commute fee reimbursement Internet and phone bills covered Compensation Philosophy Best Offer Upfront : Choose from three cash-equity balance options, no negotiation needed. Top 1% Talent : Above-market pay (top 5 percentile) to attract high performers. High Ownership: Small teams, >$1M revenue/employee, and significant equity. Performance-Based : Offers tied to interview performance, not experience or past salaries. Interview Process Online Assessment (25-30 min) : One HackerRank coding questions on practical problem-solving (7 days to complete). Technical Phone Interview 1 (30 min) : Live coding on CoderPad, focusing on data structures and algorithms. Technical Phone Interview 2 (30-45 min) : Deeper CoderPad session on algorithmic thinking and coding fluency. Onsite/Virtual Interviews (2-3 hrs) : Hosted in our office if located in the Bay Area or virtual, with three rounds: Practical Coding: Tackle real-world coding tasks with debugging in a basic environment set up like Python Flask or Node.js Express, etc. System Design: Architect a production-ready system. Tools & Automation: Build automations or improve workflows in any basic environment setup like Python Flask or Node.js Express, etc. Learn More Retell AI - API That Turns Your LLM Into A Human-Like Voice Agent Retell AI Basics: Everything You Need to Start Building Voice Agents Join Retell AI to build the future of voice automation, shipping impactful code and defining a new standard for AI-driven communication. Seniority level Seniority levelMid-Senior level Employment type Employment typeFull-time Job function IndustriesTechnology, Information and Internet Referrals increase your chances of interviewing at Retell AI by 2x Inferred from the description for this job Medical insurance Vision insurance Get notified about new Software Engineer jobs in San Francisco Bay Area . San Francisco, CA $160,000.00-$180,000.00 5 days ago Software Engineer, AI Intern (Fall 2025) San Francisco Bay Area $57.00-$61.00 2 weeks ago San Francisco, CA $40,000.00-$70,000.00 2 weeks ago San Francisco, CA $145,000.00-$230,000.00 3 days ago Mountain View, CA $125,400.00-$188,100.00 2 weeks ago Software Engineer, AI Platform - New Grad San Francisco, CA $130,000.00-$238,000.00 1 day ago San Francisco, CA $220,000.00-$350,000.00 2 weeks ago San Jose, CA $130,000.00-$180,000.00 2 weeks ago San Francisco, CA $130,000.00-$140,000.00 3 hours ago Mountain View, CA $130,000.00-$176,000.00 1 week ago Software Engineer (L4), Content & Business ProductsSoftware Engineer, Frontend (All Levels) San Francisco, CA $150,000.00-$220,000.00 2 weeks ago San Francisco, CA $150,000.00-$230,000.00 2 months ago Full Stack Software Engineer - Post-training San Francisco, CA $150,000.00-$283,000.00 2 weeks ago (General Hire) Software Engineer Graduate (Advertisement Team) - 2025 Start (BS/MS) San Jose, CA $113,500.00-$250,000.00 2 weeks ago Full Stack Software Engineer (L4), Product Localization Engineering San Francisco, CA $130,000.00-$240,000.00 6 days ago New Grads 2025 - Software Engineer, Algorithm San Jose, CA $120,000.00-$165,000.00 9 months ago Palo Alto, CA $152,400.00-$228,700.00 2 weeks ago We're unlocking community knowledge in a new way. Experts add insights directly into each article, started with the help of AI.

Founding Senior Machine Learning Engineer Join to apply for the Founding Senior Machine Learning Engineer role at Retell AI. Base pay range $200,000 - $280,000 per year About Retell AI Retell AI is using first principles to reimagine the call center with cutting edge voice AI. We believe voice is still the most natural way humans communicate, yet it has been trapped in outdated call centers for decades. Our mission is to bring intelligence, empathy, and speed to every phone conversation between businesses and their customers. Since launching 18 months ago, 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, Altman Capital, and other leading investors, we have scaled to $30M ARR with a team of 20 people, up from $5M at the start of 2025. Now, we're scaling fast, and we're looking for bold, ambitious people to help us build the gold standard for voice automation. If you want to work on deeply technical challenges, move fast, and make an outsized impact at one of the fastest growing Voice AI startups in the world, you'll love it here. Let's build the future of voice automation together. We're a top 50 AI app in a16z list: We're also one of the top ranking startups on: About the Role This is a hands on, high ownership role for ML engineers who want to build production models that actually ship and perform under real world constraints. As a Founding Senior Machine Learning Engineer at Retell, you'll work across the ML stack to power human like voice agents that handle millions of real time phone conversations. You'll fine tune large language models and audio models, evaluate them with rigorous benchmarks (and human feedback), and deploy them into latency sensitive, high traffic systems. You'll own model performance end to end-from training pipelines to post deployment monitoring-and shape our ML strategy alongside the founding team. If you're excited by hard technical challenges, fast iteration, and the opportunity to define how voice AI works at scale, this role is a rare chance to do it from the ground up. Key Responsibilities Train & Tune Models - Fine tune LLMs and audio models to maximize speed, accuracy, and production readiness-pushing the frontier of real time AI voice experiences. Benchmark & Evaluate - Build datasets, define rigorous metrics, and measure model performance across high impact voice AI tasks to guide development. Deploy to Production - Work closely with engineering to ship models, monitor them in the wild, and ensure they stay fast, reliable, and accurate at scale. Run Human Evaluations - Build scalable pipelines to collect structured human feedback, benchmark subjective quality, and inform model iterations. Level Up Infrastructure - Design and maintain the ML infrastructure needed for fast experimentation, robust training, and continuous deployment. YOU MIGHT THRIVE IF YOU ML Engineer with Real World Experience - You've trained and shipped models in production. Bonus if you've worked with LLMs or audio models. Fluent in Modern ML Stack - You know your way around Python, PyTorch, and today's ML tools-from training pipelines to evaluation benchmarks. Execution Oriented - You move fast, take ownership, and focus on solving real problems over perfect ones. Startup Ready - You're adaptable, resilient, and energized by ambiguity and fast changing priorities. Clear Communicator & Team Player - You collaborate well across functions and push decisions forward. JOB DETAILS Cash: $200,000 - $280,000 base salary Equity: 0.15% - 0.35% Location: Redwood City, CA, US US Visas: Retell AI is open to sponsoring work authorization for qualified candidates, including H1B/H-1B, TN, L-1, E-3, F-1 (OPT/CPT), and O-1 visas. Other Benefits 100% coverage for medical, dental, and vision insurance $70/day DoorDash credit for unlimited breakfast, lunch, dinner, and snacks $200/month wellness reimbursement (gym, fitness classes, etc.) $300/month commuter reimbursement (gas, Caltrain, etc.) $75/month phone bill reimbursement $50/month internet reimbursement Compensation Philosophy Best Offer Upfront: Choose from three cash equity balance options, no negotiation needed. Top 1% Talent: Above market pay (top 5 percentile) to attract high performers. High Ownership: Small teams, >$1M revenue/employee, and significant equity. Performance Based: Offers tied to interview performance, not experience or past salaries. INTERVIEW PROCESS Online Assessment (30 min): Coding questions on practical problem solving (7 days to complete). Talent Screen (15 min): Chat with our recruiter to get a better sense of the role, the team, and what it's like to work here. Technical Interview (45 min): Machine Learning specific coding interview. Technical Interview (45 min): Live Practical Systems Design and Coding interview. Onsite/Virtual Interviews (3 hrs): Hosted in our office if located in the Bay Area or virtual, with three rounds: ML System Design: A non coding interview focused on white boarding and high level system architecture. ML Question Deep Dive: In depth discussion exploring your approach to a machine learning problem. Backend + AI Practical: A hands on coding interview combining backend development with AI integration. Offer: Final stage, pending decision and offer discussion.