Software Engineer, Agent Harness

About Cartesia Our mission is to architect AI that learns from and interacts with the world like humans do. We're pioneering the model architectures that will make this possible. Our founding team met as PhDs at the Stanford AI Lab, where we invented State Space Models or SSMs, a new primitive for training efficient, large-scale foundation models. Our team combines deep expertise in model innovation and systems engineering paired with a design-minded product engineering team to build and ship cutting edge models and experiences. We're funded by leading investors at Index Ventures and Lightspeed Venture Partners, along with Factory, Conviction, A Star, General Catalyst, SV Angel, Databricks and others. We're fortunate to have the support of many amazing advisors, and 90+ angels across many industries, including the world's foremost experts in AI. About the Role Cartesia builds real-time multimodal intelligence: fast, state-of-the-art voice models, and the platform that puts them into production. We started as a research lab, pioneered the state space model architecture, and now we're bringing that research to customers through Managed Agents, our voice agents product. In this role, you'll build the platform behind Managed Agents. Customers rely on our stack to run real-time, production-grade voice agents. You'll own the stack end-to-end and directly shape the latency, reliability, and developer experience of every agent built on Cartesia. Your Impact Evolve the realtime transport layer that carries audio between users and agents, expanding how customers connect across web, SDKs, and telephony without regressing latency or quality. Trace and cut end-to-end conversational latency across the STT, LLM, and TTS pipeline. Make agent deployments fast and resilient: faster cold starts, smarter scaling, graceful behavior under load. Define how voice agent quality is measured, building eval suites, LLM-as-judge scoring, and regression tracking that catch quality and latency regressions before they ship. What You Bring Experience building and operating distributed backend systems in production, ideally at a high-growth startup. We care more about what you've shipped than strict years of experience. Strong product instincts: you think in customer-facing latency, reliability, and developer experience, and you have opinions on what to build and why. Fluent use of coding agents and a habit of keeping pace with the frontier. Clear communication with technical and non-technical audiences, sharp specs, and a strong presence in design reviews. Nice-To-Haves Experience with real-time media systems in production, including WebRTC, SIP, RTP, or low-latency audio. Experience with voice agents or agent frameworks such as Pipecat, LiveKit, OpenAI Agents SDK, Claude SDK, or Vercel AI SDK. Experience building developer-facing platforms or infrastructure, such as SDK backends or API platforms. Experience with distributed systems at scale, including high-throughput workloads, autoscaling, multi-region architectures, or queue-based systems. Note: Cartesia participates in E-Verify and will provide the federal government with Form I-9 information to confirm employment eligibility after hire. More Details 🏢 In-office policy: We’re an in-person team based out of offices in 🇺🇸 San Francisco, 🇬🇧 London and 🇮🇳 Bangalore. We love being in the office, hanging out together, and learning from each other every day. 🌎 Visa sponsorship: We provide visa sponsorship support and assess each circumstance on a case-by-case basis. However, visa sponsorship is dependent on many factors, including the role you are applying for, and the location you are going to be based, and so we can't always guarantee success. Your Recruiter will work with you to understand your visa sponsorship needs from the first call. 🚢 We ship fast. All of our work is novel and cutting edge, and execution speed is paramount. We have a high bar, and we don’t sacrifice quality or design along the way. 🤝 We support each other. We have an open & inclusive culture that’s focused on giving everyone the resources they need to succeed. Our Benefits (US Employees Only) 💰 Compensation Competitive base salary alongside attractive equity package. 🩺 Health Insurance Fully covered medical insurance along with dental and vision for you and your family. 🧑‍🧑‍🧒‍🧒 Parental Leave 9 weeks paternity & 12 weeks maternity leave 🏦 401(k) 🚆 Commuter Allowance A monthly stipend to help you get to and from the office. 🏖️ Flexible PTO Take as much time as you need to recharge your batteries. 🍲 Meals & Snacks Lunch, dinner and plenty of snacks, provided daily. 🦖 Your own personal Yoshi Our Commitment to Equal Opportunity Cartesia is an equal opportunity employer. We consider qualified applicants without regard to race, color, religion, sex, national origin, age, disability, veteran status, genetic information, or any other legally protected status.