SAN FRANCISCO — Opendoor, a start-up that flips homes, attracted attention in June when it announced it had raised $325 million from a long list of venture capitalists. The financing valued the four-year-old company at more than $2 billion.

That was only an appetizer. Three months later, Opendoor has more than doubled its cash pile. On Thursday, the company said it had gotten a $400 million investment from SoftBank’s Vision Fund. The valuation for Opendoor remains the same.

The so-called mega-round for Opendoor was not the Vision Fund’s only major real estate-related deal on Thursday. The firm also co-led a $400 million investment in the high-end brokerage Compass that valued the company at $4.4 billion.

The hauls are part of a race by investors to pour money into technology for real estate, or what Silicon Valley now calls proptech.