Tesla Is Coming Out With Something Called D. Nobody Knows What It Is.

For a car company with exactly one model in production, Tesla sure manages to make a lot of headlines. The latest flurry came after Elon Musk teased his million-plus Twitter followers with the following tweet Wednesday evening:

The company has followed up by sending invitations to the press for an event at 7 p.m. on Oct. 9 at Hawthorne Airport, near the headquarters of Musk’s other venture, SpaceX.

So what is the D? What is the “something else?” No one outside the company seems to know for sure, but the tweet nonetheless boosted Tesla’s already stratospheric stock prices by nearly 5 percent.

That seems like an overreaction, given what the D almost certainly isn’t: an entirely new model of car. Tesla’s plans in that direction have been well-mapped for years now. Its Model X SUV, adapted from the Model S platform, is expected to enter production next year, with the all-new Model 3 to follow a few years later, after Tesla finishes building the world’s largest electric-car battery factory.

Rather, speculation is that the D involves some form of modification or update to the Model S, since that’s what the car in the photo appears to be. The leading theory so far is that the D will be an all-wheel-drive version of the sedan, with “D” perhaps standing for “dual motor”—one for the front axle, one for the rear. An AWD Model S has been rumored since The Verge reported more than a year ago that Tesla was working on one. Presumably, the company has already been working on AWD technology in preparation for the forthcoming Model X.

Bolstering that theory is a tweet from an Edmunds editor at the ongoing Paris Motor Show who spotted a model guide for the event that listed a Tesla “Model S All Wheel Drive” among the cars expected to be on display. The car has not materialized thus far, but the show officially starts Saturday and runs through October 19, so perhaps the company is just keeping it under wraps until after the U.S. unveiling.

Why all-wheel drive? Beyond making the car more practical in rain and snow, it could make the top-end Model S’s already neck-snapping acceleration even snappier. The 85KwH Model S goes from 0 to 60 in 4.2 seconds. An all-wheel-drive edition might just do it in under 4, putting the four-door sedan in a class with the very sportiest of supercars.

A second plausible hypothesis is that either the D or the “something else” could be related to computer-assisted driving features. Musk has expressed interest in an autonomous Tesla in the past, and recently the first driver-assist features have begun to pop up on the Model S. So far they include a system that alerts you with a rumble when you drift from your lane and a “speed assist” that can let you know when you’re breaking the speed limit. That’s pretty basic stuff so far, but it wouldn’t be a surprise to see Tesla introduce some more innovative features in the years to come.

Are there other possibilities for Thursday’s announcement? Going on the photo alone, one might think that the secret lies somewhere on the upper half of the car. Could we see a Model S convertible—a drop-top, if you will? Probably not, but it’s a fun thought. Business Insider’s Matthew DeBord has an amusing list of even-less-plausible ideas, from an updated Tesla Roadster to a diesel-powered Tesla to one that runs entirely on D batteries.

It’s also possible at least one of the announcements will not be a car at all. The Wall Street Journal reminds us that Musk told it last month to expect “significant” product news in the near future that does not involve a new vehicle.

Whatever the news turns out to be, Musk’s tweet is further proof that the man is not only a technological visionary but a talented showman. AdAge and others were quick to note the resemblance of his “something else” teaser to Steve Jobs’ famous “one more thing” line at Apple launch events.

When Jobs died, pundits looked to other technology giants for a spiritual successor. Few guessed that the most iconic CEO of the 2010s would be found behind the wheel of a car company.

Previously in Slate: