Senior Software Engineer, Applied AI

About Mainstay

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!

About the role

What you should expect as a full-stack senior software engineer - maximum agency, tight feedback loops with customers, and no shortage of product challenges that directly translate to business value! You’ll have the opportunity to design, build, and ship complex AI-powered workflow management systems and tools that enable our operations team to execute at scale.

We’re looking for someone who can both fine-tune and optimize models and ship reliable, production ready AI features end to end - from retrieval pipelines and guardrails to backend systems and user facing product experiences.

Our products are built with Python, Typescript, and React on AWS.

What you'll do

In this role, you’ll be responsible for both shaping new AI-powered product experiences and ensuring they’re reliable at scale. That means fine-tuning and optimizing models for our domain, designing retrieval pipelines and guardrails, and building the backend systems that make these features production-ready. You’ll work closely with product managers, designers, and operators to bring AI features from idea to launch, balancing innovation with stability.

In this role, you will:

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-tuning 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 we're looking for

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

Strong full-stack engineering skills with a focus on scalable systems and adaptability

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

Bonus points if

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

#LI-AW

Mainstay Built on Trust

At Mainstay, trust is at the core of everything we do. We build trust with everyone - from candidates to employees to partners. We believe in fairness and openness throughout our hiring process, evaluating candidates based on qualifications without regard to race, color, religion, national origin, age, gender, marital status, disability, veteran status, sexual orientation, gender identity, or any other protected status. Our privacy practices describe how we handle applicant information, you can find the policy details for California residents here.

We are committed to providing reasonable accommodations throughout our recruitment processes for candidates with disabilities, pregnancy, religious beliefs, or other reasons protected by applicable laws. If you require assistance or a reasonable accommodation, please contact us at mainstay-recruiting@opendoor.com

Compensation Range: $172.1K - $248K