Senior Software Engineer, Applied AI

Mainstay Labs Inc.

72d

About The Position

Mainstay is the leading market intelligence platform purpose built for buying, managing, and selling homes in the single family rental industry. As an AI native company, we turn complex data into clarity that helps the industry move forward with confidence. Founded within Opendoor, Mainstay launched as an independent company in 2024 and recently raised a Series A round led by Khosla Ventures. Ready to shape the future of real estate with AI? Join Mainstay and help us redefine what’s possible in the single family rental space. If you thrive on solving complex problems and want to make a tangible impact in a fast-growing industry, we’d love to hear from you - apply now and let’s move the industry forward, together!

Requirements

• 5+ years of experience building and delivering production-grade software, ideally in fast-paced, high-growth startup environment
• At least 3 years of hands-on experience developing and deploying production-ready AI features (LLM applications, fine-tuning, RAG systems, guardrails, evals, etc.)
• Strong full-stack engineering skills with a focus on backend scalability and system reliability
• Experience fine-tuning and deploying LLMs
• Deep understanding of LLM evaluation methods, including prompt testing, retrieval precision, hallucination detection, and cost/performance tradeoffs
• Experience building custom eval pipelines using techniques like model-as-a-judge or embedding similarity
• Hands-on work with agentic frameworks (e.g. LangGraph, AutoGen, CrewAI) or custom agent systems
• Clear, concise communicator - essential for our remote, highly collaborative team
• Proactive and ownership-driven - comfortable navigating ambiguity and shifting priorities
• Customer-focused mindset with a drive to build solutions that solve real problems
• Experience with AI/ML tools or APIs; bonus if you’ve worked with Python-based RAG, voice agents, or AI task automation

Nice To Haves

• Experience working with retrieval-augmented generation (RAG) pipelines
• Exposure to building or integrating voice agents
• Familiarity with task automation powered by AI
• Strong Python background with applied AI or ML workflows

Responsibilities

• Contribute to all phases of product development, from ideation and prototyping to implementation and iteration
• Build and evolve both frontend product experiences and backend services that power them
• Fine-tune existing models and optimize their performance for Mainstay use cases
• Design reliable, scalable backend services to support AI-powered features in production
• Leverage AI to modernize and automate legacy workflows in the real estate industry
• Evaluate and benchmark LLM performance across latency, cost, accuracy, and hallucination rates
• Tune prompts, chain-of-thought logic, and implement retrieval strategies such as RAG and vector stores
• Monitor performance, safety, and cost of LLM-driven features in production environments
• Define and build useful LLM-powered experiences in partnership with cross-functional teams
• Mentor and support the growth of other engineers on the team
• Collaborate closely with product managers, designers, and operators to identify and solve customer pain points

What This Job Offers