Musk called the moment the "culmination of a decade of hard work" in a post on his social media platform X and noted "the AI chip and software teams were built from scratch within Tesla".
Teslas were spotted in an Austin neighbourhood called South Congress with no one in the driver's seat but one person in the passenger seat.
The automaker planned a small trial with about 10 vehicles and front-seat riders acting as "safety monitors", though it remained unclear how much control they had over the vehicles.
In recent days, the automaker sent invites to a select group of influencers for a carefully monitored robotaxi trial in a limited zone.
The rides are being offered for a flat fee of $US4.20 ($A6.50), Musk said on X. Tesla investor and social media personality Sawyer Merritt posted videos on X showing him ordering, getting picked up and taking a ride to a nearby bar and restaurant using a Tesla robotaxi app.
If Tesla succeeds with the small deployment, it still faces major challenges in delivering on Musk's promises to scale up quickly in Austin and other cities, industry experts say.
It could take years or decades for Tesla and self-driving rivals, such as Alphabet's Waymo, to fully develop a robotaxi industry, said Philip Koopman, a Carnegie Mellon University computer-engineering professor with expertise in autonomous-vehicle technology.
A successful Austin trial for Tesla, he said, would be "the end of the beginning - not the beginning of the end".
Most of Tesla's sky-high stock value now rests on its ability to deliver robotaxis and humanoid robots, according to many industry analysts. Tesla is by far the world's most valuable automaker.
The Tesla robotaxi rollout comes after more than a decade of Musk's unfulfilled promises to deliver self-driving Teslas.
Musk has said Tesla would be "super paranoid" about robotaxi safety in Austin, including operating in limited areas.
The service in Austin will have other restrictions as well. Tesla plans to avoid bad weather, difficult intersections, and will not carry anyone below age 18.
