Tesla stock was down, a little, to start Wednesday trading after a surprise announcement from CEO Elon Musk about the company's Full Self-Driving driver assistance product.

Shares of the electric-vehicle maker were off 0.7% at $444.25, while S&P 500 and Dow Jones Industrial Average futures were down 0.4% and 0.3%, respectively.

The move came after Musk announced on his social-media platform, X, that Tesla would stop selling FSD for a one-time payment and go to a subscription-only option.

FSD is Tesla's highest-level driver assistance product that can do most of the driving. It still requires human supervision 100% of the time, but Tesla owners and investors are hopeful that the system will become ' eyes-off' at some point this year in certain conditions. The car would be allowed to do some of the driving without supervision.

FSD currently costs $8,000 once or $99 a month. That makes the break-even point between subscription and purchase at 81 months, or almost seven years. If you own a Tesla longer than that and want FSD, a one-time purchase is the better option.

Tesla has hundreds of thousands of FSD subscribers. It didn't respond to a request for comment about the number of users or how they pay. It's likely the majority are monthly subscribers.

How customers choose to pay for FSD isn't as important as the technology itself. Self-driving cars are a big deal to Tesla. The company launched a robo-taxi service in Austin, Texas, in June.

Wedbush analyst Dan Ives projects Tesla's robo-taxis will expand to some 30 additional cities in 2026 and believes the self-driving opportunity for the company is worth a trillion dollars.

He is the biggest Tesla bull, rating shares Buy, with a Street-high price target of $600 a share.

Others have big robo-taxi expectations, too. Wolfe Research analyst Emmanuel Rosner projects $6 billion in FSD revenue by 2028. What's more, he projects $60 billion in robo-taxi earnings before interest, taxes, depreciation, and amortization, or Ebitda, by 2035.

Rosner rates Tesla stock Hold and doesn't have a price target for shares.

Regardless of the rating, everyone on Wall Street, including investors, needs a view on FSD to understand and value Tesla stock.

Coming into Wednesday trading, Tesla's stock was down about 1% this year and up about 11% over the past 12 months.