The price of a Tesla vehicle equipped with “full self-driving” is about to get more expensive, the second time in the past several months the company has increased fees for a feature that isn’t completely functional.

Tesla CEO Elon Musk tweeted Tuesday that the price of its full self-driving option will increase by $1,000 on August 16. Full self-driving, or FSD — a feature that Musk promises will one day deliver full autonomous driving capabilities — currently costs $6,000.

Cost of Tesla full self-driving option increasing by ~$1000 on August 16 — Elon Musk (@elonmusk) July 16, 2019

Musk has previously said the price of FSD will “increase substantially over time.” The first increase, which raised the price from $5,000 to $6,000, went into effect May 1. In previous tweets, Musk has said the total increase would be “something like” around the $3,000+ figure. This means buyers should prepare for more price hikes even after this latest one.

It’s a strategy that Musk repeated on Tuesday, noting in an additional tweet that the “cost of the Tesla FSD option will increase every few months. Those who buy it earlier will see the benefit.”

As mentioned earlier this year, cost of the Tesla FSD option will increase every few months. Those who buy it earlier will see the benefit. — Elon Musk (@elonmusk) July 16, 2019

Tesla vehicles are not self-driving. Musk has promised that the advanced driver assistance capabilities on Tesla vehicles will continue to improve until eventually reaching full automation.

Today, Tesla vehicles come standard with Autopilot, an advanced driver assistance system that offers a combination of adaptive cruise control and lane steering. Tesla once charged for this feature as well, but made it standard in April 2019.

The more robust and higher-functioning version of Autopilot is called full self-driving. FSD includes the parking feature Summon as well as Navigate on Autopilot, an active guidance system that navigates a car from a highway on-ramp to off-ramp, including interchanges and making lane changes. Once drivers enter a destination into the navigation system, they can enable “Navigate on Autopilot” for that trip.

Tesla announced in October 2016 that all of its cars would come equipped with the hardware necessary for so-called “full self-driving.” The company has since modified the hardware needs with the addition of a new custom computer chip that all new vehicles have come equipped with since spring 2019.

It’s been nearly three years since Tesla began charging for an option that would eventually deliver an autonomous driving experience. And customers are still waiting.

Tesla does continue to improve Navigate on Autopilot and the broader FSD system through over-the-air software updates. The company says on its website that FSD will soon be able to recognize and respond to traffic lights and stop signs and automatically drive on city streets.