James Martin/CNET

In a tweet mentioning @TeslaMotors, Tesla CEO Elon Musk promised a big announcement on Thursday, and wrote, "Am going to put my money where my mouth is in v major way."

A Tesla spokeswoman told CNET that the company is still working out the place and timing of the announcement. However, she said that Tesla will not be at the New York auto show, which is holding a press preview on Wednesday and Thursday of this week.

After the tweet was posted, Tesla's shares jumped 4.23 percent.

Musk's second sentence in the tweet suggests he is backing something he said previously. At a press conference at the Geneva auto show earlier this month, Musk said the company's Supercharger network, fast chargers for the Tesla Model S, would be free to use for Tesla owners for life. He also said that solar cells installed at the Superchargers would make it so Tesla would not have to buy electricity from a utility.

Given that history, it seems likely Thursday's announcement might have something to do with the Supercharger network.

Tesla's Model S has reached full production from its Fremont, Calif., manufacturing plant. Tesla's year-end shareholder statement said that the next car, the Model X, would be delayed one year. Tesla has previously said it would eventually add a more affordable electric car to its lineup, but it seems unlikely that Thursday's announcement would have anything to do with that.