Tesla owners will soon be able to add autopilot functionality to their vehicles if they weren't able to sign up for it earlier, company chief executive Elon Musk said Tuesday.

Drivers will be allowed to unlock Tesla's autopilot with a $3,000 payment, Musk told investors. That's about $500 more than what early adopters paid for autopilot's most powerful capabilities.

"That's something we'll be allowing people to do at some point in the coming months," said Musk. "Sort of like an in-app purchase, I guess."

All Tesla vehicles already benefit from some autopilot safety features, thanks to a recent software update. Automatic emergency braking, collision avoidance and collision warning have now rolled out across the fleet, Musk said. But only about 40,000 Teslas have autopilot enabled, he added. Those vehicles are collectively logging a million miles of driverless driving a day, giving Tesla valuable usage data.

The decision by Tesla to allow "in-app purchases" of a sort highlights the company's growing habit of using software to upgrade its vehicles, equipping them with new powers on a rapid update cycle.

Now, by giving drivers the additional ability to unlock new features on demand, Tesla is hinting at a future where owners could pick and choose which new services they would like to enable, and when. That's a further advance over simply rolling out system updates to the entire fleet at once (already a novel step for the automotive industry).