Unlocking Real Estate's Back Office: Mainstay Secures $18M and Acquires Truelist

SAN FRANCISCO – September 16, 2026 – The physical landscape of residential real estate is defined by concrete, wood, and steel, but the systems that actually govern it are built on a fragile foundation of fragmented data, localized bureaucracy, and manual paperwork. Today, Mainstay, an intelligent system of record designed to automate the lifecycle of residential assets, announced it has raised over $18 million in growth capital. Alongside the funding, the company has acquired Truelist, an AI-powered listing platform tailored for brokers and agents.

The financing round was led by new investors Parker89, Stackpoint, Alpaca VC, and FJ Labs, with participation from existing backers Khosla Ventures, Era Ventures, and Clocktower Technology Ventures. The capital injection brings Mainstay’s total funding to approximately $45 million since its formal carve-out from Opendoor in August 2024. The acquisition of Truelist, coupled with the appointment of its founder Carey Armstrong as Chief Strategy Officer, signals a pivotal expansion for Mainstay. The company is actively bridging the gap between the sophisticated automation tools used by institutional mega-landlords and the everyday workflows of independent real estate brokerages.

From iBuying to B2B Infrastructure: The Opendoor Diaspora

To understand Mainstay’s architecture, one must look at its origins inside the high-stakes world of iBuying. Founded by former Opendoor executives Dod Fraser, J.D. Rasmussen, and Michael Dulfer, Mainstay began its life as an internal enterprise unit. During the peak years of algorithmic home flipping, Opendoor realized that the true bottleneck to scale was not acquiring properties, but managing the staggering administrative burden of holding them.

Tracking property taxes across thousands of jurisdictions, clearing Homeowners Association (HOA) violations, and managing utility transfers required an army of operators. By automating these backend processes, the team inadvertently built a highly scalable, high-margin software product hidden inside a capital-intensive real estate company. Today, Mainstay operates as an independent entity, servicing 95% of the 60 largest residential real estate investors and facilitating more than $12 billion in cumulative transaction volume.

“Residential real estate is still run across an enormous number of disconnected systems, datasets, and manual workflows,” said Dod Fraser, CEO and Co-Founder of Mainstay. “We have spent years building the technology to seamlessly connect data, decisions, and execution for the largest residential investors. This capital and the acquisition of Truelist allow us to bring that same infrastructure to a much broader market of brokerages, agents, and investors.”

Agentic AI Meets the 50,000-Portal Problem

The most compelling aspect of Mainstay’s platform is its claim of executing over 2 million agentic workflows across more than 50,000 external portals. In the realm of property technology, this is a monumental technical hurdle. The US residential market is notoriously decentralized, governed by roughly 600 Multiple Listing Services (MLSs), 3,143 distinct county tax assessment offices, and over 250,000 localized HOAs.

Historically, software providers attempted to solve this fragmentation using Robotic Process Automation (RPA)—essentially programming bots to click specific buttons on web pages. However, as one enterprise real estate architect noted, RPA is incredibly brittle; the moment a county clerk updates their website's layout, the bot breaks.

Mainstay bypasses this limitation by utilizing multi-modal large language models (LLMs) and computer-use agents trained on years of proprietary operational logs. Instead of following rigid click-paths, these agentic bots can visually interpret unstructured PDF statements, navigate non-standard municipal web forms, and file automated property tax assessment protests. When a task hits a high-liability threshold—such as finalizing a payment transfer—the system flags the anomaly for human-in-the-loop validation. It is a pragmatic application of AI that replaces bureaucratic busywork rather than attempting to replace the real estate agent entirely.

Wall Street Tech for Main Street Brokers

While Mainstay has dominated the institutional single-family rental (SFR) market, the acquisition of Truelist represents a strategic pivot toward the retail brokerage sector. Truelist was launched to help brokers and agents create, manage, and distribute listings with greater consistency and control. By folding Truelist into its core engine, Mainstay is effectively democratizing institutional-grade data.

This merger also represents a fascinating convergence of two prominent proptech talent networks: the "Opendoor Mafia," characterized by heavy operational and backend infrastructure, and the "Zillow Mafia," known for high-margin consumer portals and agent monetization. Carey Armstrong, the incoming Chief Strategy Officer at Mainstay, previously served as Vice President of Zillow’s Premier Agent business and co-founded the digital mortgage startup Tomo. Her expertise in the agent-facing ecosystem provides the exact retail translation layer that Mainstay’s institutional engine requires.

“Mainstay and Truelist are both unusual in that their teams have actually built and operated these systems at scale inside the industry’s largest and most innovative residential platforms,” said Clelia Peters, Managing Partner of Era Ventures and a Mainstay board member. “The combination of deep residential real estate experience, a well of proprietary data, and an innovation and AI first approach is unique in the industry, and creates an opportunity to build something foundational.”

Bridging the Real Estate Divide

For decades, a stark technological divide has existed between Wall Street-backed SFR operators and Main Street independent brokers. Mega-landlords possessed automated data toolkits for predictive pricing, instant tax histories, and automated compliance, while local agents were left manually pulling records from disjointed county websites and antiquated MLS portals.

By integrating Truelist’s listing management interface with Mainstay’s autonomous execution engine, the combined platform aims to level the playing field. Agents can now access the same backend automation that powers the largest institutional portfolios, reducing manual data entry and ensuring compliance across fragmented local systems.

“Mainstay and Truelist have been attacking the same broken system from different angles – Mainstay on behalf of investors, Truelist on behalf of brokers and agents,” said Carey Armstrong. “Joining forces means we stop duplicating effort and start compounding it. I have enormous respect for what Dod and the team have built, and I’m excited about what we can do together.”

As the real estate industry continues to navigate shifting commission structures and an unpredictable interest rate environment, the focus of innovation has clearly moved from consumer-facing disruption to foundational infrastructure. Mainstay’s latest evolution suggests that the next generation of proptech unicorns won't be built by changing how people buy homes, but by quietly and autonomously fixing the complex systems that make those transactions possible.