Alphabet’s driverless car unit now has vehicles operating in San Francisco, Phoenix and Los Angeles.

Amid its push to grow its fleet of autonomous robot taxis and expand into new cities, Waymo has raised $5.6 billion from outside investors, its largest funding round to date.

Waymo’s parent company, Alphabet, led the round, which included investments from Andreessen Horowitz, Fidelity, Perry Creek, Silver Lake, Tiger Global and T. Rowe Price, according to a statement.

The fresh money comes behind Waymo’s first taste of commercial success. Its robot taxis are now completing over 100,000 rides each week in San Francisco, Phoenix and Los Angeles, double its number in May, and will be operating in Austin, Texas, and Atlanta by 2025 through a partnership with Uber.

Waymo has raised outside investment twice before — $2.25 billion in 2020 and $2.5 billion in 2021. The most recent round was oversubscribed, the company said, and it did not disclose Waymo’s valuation or how much of the round Alphabet accounted for. On a July earnings call, Alphabet executives said the company planned to invest an additional $5 billion in Waymo over the coming years.

Investors in the round are “not looking for a quick turnaround on their money,” said Chris Ballard, a managing director at Check Capital Management, an investment firm. “These are long-term firms that want a much bigger payoff over a much longer period of time.”

The company has plenty of competitors, including Tesla and its newly unveiled robot taxis, Zoox from Amazon and the General Motors service Cruise. Waymo is not yet profitable, but as of now, it easily has the most self-driving robot taxis actively on the road.

Its current fleet of vehicles are electric Jaguar I-Paces, but Waymo announced a partnership with Hyundai this month and started testing its vehicles made by Zeekr, a Chinese electric automaker, in July.