Mainstay Raises $18M Series C+ for Residential Real Estate Platform

Mainstay, the intelligent system of record for residential real estate, has raised $18 million in a Series C+ round. The funding was announced on September 16, 2026.

What Mainstay Does

Mainstay combines each customer's data with proprietary data and thousands of external sources into a single, continuously updated record. That record is used to underwrite, price, and execute workflows across buying, owning, and selling homes.

The company's agentic platform automates tasks such as:

Transaction execution
Property taxes
HOA management
Payments

Mainstay serves institutional investors and property managers, including 95% of the 60 largest residential real estate investors. Following its 2026 acquisition of Truelist, the company also serves brokerages and agents.

Company Background

Mainstay was carved out of Opendoor as an independent company in August 2024. It has facilitated more than $12 billion in residential transactions. The company is led by CEO and co-founder Dod Fraser, Opendoor's former President.

The Round

Round type: Series C+
Amount: $18 million
Date: September 16, 2026

Investors in the round include Khosla Ventures, FJ Labs, Era Ventures, Clocktower Technology Ventures, Alpaca VC, Parker89, and Stackpoint. No lead investor was disclosed.

Why It Matters

Mainstay's position as a system of record for residential real estate gives it a central role in how institutional investors and property managers underwrite and execute transactions. The platform's agentic automation targets back-office and operational workflows that are typically fragmented across multiple systems.

The 2026 acquisition of Truelist extended Mainstay's reach into brokerages and agents, broadening its customer base beyond institutional investors and property managers. With more than $12 billion in facilitated transactions, the company has established meaningful scale in a segment where data accuracy and workflow automation are critical.

Company Snapshot

Company: Mainstay
Domain: mainstay.io
Stage: Series C+
Sector: Residential real estate technology
Leadership: Dod Fraser, CEO and co-founder

For acquisition watchers, Mainstay sits at the intersection of proptech infrastructure and agentic automation, serving a concentrated base of large institutional customers while expanding into the brokerage and agent market.