The investment round was led by Google-parent Alphabet, which spun the company off from a research unit and retains controlling interest, according to Waymo.

The list of Waymo backers includes Silicon Valley venture capital powerhouse Andreessen Horowitz, along with Fidelity and Silver Lake.

Waymo declined to disclose the value placed on the company during the investment round.

It raised $3.2 billion in 2020 and $2.5 billion in 2021.

Waymo started as a "moonshot" project in Google's X lab in 2009 and was spun off into a separate company in 2016.

Waymo One ride-hailing services operate in San Francisco, Phoenix, and Los Angeles, with the company saying it plans to expand to the cities of Austin and Atlanta as part of a partnership with ride-share platform Uber.

"The company has built the safest product in the autonomous vehicle ecosystem, as well as the best," said Chase Coleman, founder of Tiger Global, which took part in the latest investment round.

Coleman credited Waymo with being able to "balance ambitious goals with responsible execution."

While Waymo competitors include General Motors subsidiary Cruise, as well as Amazon-owned Zoox, it has been moving steadily along the road to making robotaxis more common.

Elon Musk recently unveiled what he said was a robotaxi capable of self-driving, predicting it would be available by 2027 -- about a decade after he first promised an autonomous vehicle.

Waymo, on the other hand, said its robotaxi service already provides 100,000 paid rides weekly.

The National Highway Traffic Safety Administration early this year launched an investigation into Waymo after reports some self-driving cars hit stationary objects.

Robotaxis in San Francisco have also been targeted by vandals and activists opposed to the innovation.