Tesla CEO Elon Musk said the electric vehicle maker’s eagerly anticipated humanoid robot ‘Optimus’ would cost under $20,000 and cautioned it still had way to go before becoming fully functional.

“There’s still a lot of work to be done to refine Optimus and prove it,” Musk told the electric vehicle maker’s “AI Day” event being held at a Tesla office in Palo Alto, California.

Musk said existing humanoid robots are “missing a brain” — and the ability to solve problems on their own. By contrast, he said, Optimus would be an “extremely capable robot” that Tesla would aim to produce in the millions. He said he expected it would cost less than $20,000.

Tesla said the company had developed a prototype for its robot in February. That early model walked out to wave at the crowd on Friday, and Tesla showed a video of it doing simple tasks, such as watering plants, carrying boxes and lifting metal bars at a production station at Tesla’s California plant.

Musk and Tesla representatives acknowledged that there was a lot of work to be done to achieve the goal of a mass-produced, low-cost robot, using Tesla-designed technology that would be capable of replacing humans at work. Other automakers, including Toyota Motor and Honda Motor, have developed humanoid robot prototypes capable of doing complicated things like shooting a basketball, and production robots from ABB and others are a mainstay of auto manufacturing.

But Tesla is alone in pushing the market opportunity for a mass-market robot that could also be used in factory work.

A next-generation Tesla bot, which was rolled on stage by staff, will use Tesla-designed components, including a 2.3 kWh battery pack carried in its torso, a chip system and actuators to drive its limbs. The robot is designed to weigh 73 kg.