SAN FRANCISCO, March 19 (Reuters) - Uber ( UBER ) will invest up to $1.25 billion in electric vehicle maker Rivian as part of a deal in which the ride-hailing firm will start deploying 10,000 fully autonomous R2 SUVs as robotaxis from 2028, the companies said on Thursday.

Rivian's shares rose about 9% in premarket trading.

San Francisco-based Uber ( UBER ) will make an initial investment of $300 million, and will fund the remaining amount through 2031, subject to Rivian meeting certain autonomous milestones, the companies said.

Interest in driverless taxis has surged in recent months after years of missed promises, with artificial intelligence and tech partnerships offering hopes of solving complex traffic scenarios faster and mitigating high costs.

While Rivian, known for its high-end R1S SUVs and R1T pickup trucks, has not launched a robotaxi yet, it unveiled its first custom computer chip for self-driving in December. The company is also gearing up to roll out its smaller, more affordable R2 SUVs this quarter.

Meanwhile, Alphabet's Waymo, which runs about 2,500 robotaxis in several U.S. cities, has accelerated its rollouts, while Tesla has launched a small robotaxi service in Austin, Texas, with CEO Elon Musk promising rapid expansion this year.

R2 robotaxis will be available exclusively on Uber's ( UBER ) platform, starting with San Francisco and Miami, the companies said, adding that Uber ( UBER ) has the option to buy up to 40,000 more beginning in 2030.

"Should all milestones be achieved, the companies will have deployed thousands of unsupervised Rivian R2 robotaxis across 25 cities in the U.S., Canada, and Europe by the end of 2031," they said.

Uber ( UBER ) is positioning itself as a marketplace for multiple robotaxi operators, and has partnered across much of the autonomous vehicle industry, including with Waymo, Baidu and Lucid.

It is also working with Nvidia on autonomous driving, leveraging the chip designer's AI and simulation platforms to support the development and scaling of robotaxi systems.