Senior Software Engineer

• Denver/Los Angeles - Hybrid 2-day in office
• Full-time
• $160k-190k

Marvin helps people navigate their mental health and wellbeing. We partner with employers and health plans to give their members one place to understand their coverage, find care, and get support, including an AI coach built into the product. We're a small team shipping a production healthcare application, which means every engineer touches things that matter and owns them end to end.

We're hiring a senior full-stack engineer who has made AI a core part of how they build software, not a novelty. This is not a machine learning research role. You won't train models or tune GPUs. You will ship product in a modern Type Script/Next.js stack, and you'll do it with AI woven into both the product and your own workflow.

• You build with AI. You've moved well past autocomplete. You direct agentic coding tools to do real, multi-step work, you know exactly where they break, and you own every line they produce.
• You build AI into the product. You've shipped LLM-backed features to real users and lived with them in production: prompts, tool calls, evals, tracing, cost, latency, and failure modes.

• Own features end to end across our Next.js/React/Type Script app, Prisma/Postgres backend, and AWS infrastructure.
• Extend our AI coach and build new LLM-powered member experiences: retrieval over benefits data, structured extraction, guided flows, and agentic tool use against our own APIs.
• Design evaluation and observability for AI features so we know when they get worse, not just when they crash.
• Push our AI-assisted development practice forward: agent instructions, reusable skills, hooks, MCP integrations, and review practices that keep quality high as velocity climbs.
• Handle sensitive health data responsibly. PHI boundaries, redaction, audit trails, and vendor data agreements are part of the design, not an afterthought.
• Review code, whether written by a human or an agent, with a critical eye. Mentor teammates and raise the bar on testing and reliability.

• 5+ years building production web applications, with deep Type Script, React, and Node experience. Next.js is a strong plus.
• Comfort across the stack: relational data modeling (we use Prisma and Postgres), auth flows, caching, background jobs, and cloud deployment (AWS, Docker, Terraform or similar).
• A real testing habit at every layer: unit, component, and end-to-end. We use Vitest, Storybook, Cypress, and Playwright.
• Strong product judgment and the ability to work directly with design, clinical, and partner-facing teammates.

• Daily, expert use of agentic coding tools such as Claude Code, Cursor, or Codex. You write project instructions and reusable skills for your agents, hand them multi-step tasks, and review the output like a senior reviewer, not a rubber stamp.
• Hands-on experience shipping LLM features: prompt design and versioning, structured outputs, tool/function calling, streaming UIs, retrieval-augmented generation, and multi-turn conversation state.
• You've run evals and traced production LLM traffic (Lang Smith, Braintrust, Langfuse, or homegrown), and you can explain what changed the last time a model version bumped underneath you.
• You understand the cost, latency, and quality triangle and have made real trade-offs: model selection, caching, prompt compression, and fallback strategies.
• Clear-eyed about limits. You know when an LLM is the wrong tool, how to constrain one when it's the right tool, and how to keep a hallucination from ever reaching a member.

• Healthcare, benefits, or other regulated-data experience (HIPAA, SOC
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