(Reuters) -Tesla Chief Executive Elon Musk said on Tuesday that the number of robotaxis in Austin, Texas, will double in December, following the rollout of its self-driving service in the city in June.

"The Tesla Robotaxi fleet in Austin should roughly double next month," Musk said in a post on X, which is also owned by him.

It is not immediately clear how many robotaxis Tesla operates.

Tesla's robotaxi service currently operates in two cities, Austin and the San Francisco Bay Area, with safety monitors still required in the vehicles. The company last week also received a permit to operate a ride-hailing service in Arizona.

Musk said in October that he expected robotaxis to operate without safety drivers in large parts of Austin this year and that robotaxis would be operating in eight to ten metropolitan areas by the end of the year.

In July, he said he expected Tesla robotaxis to serve about half the U.S. population by year-end.

After years of missed promises and several company closures due to high costs, tight regulations and federal investigations, the robotaxi industry has rebounded with Tesla, Alphabet's Waymo, and Amazon's ( AMZN ) Zoox speeding up expansion.