Tesla CEO Elon Musk Thursday sent shockwaves through the North American trucking and business communities with a single, mid-day tweet:

“Tesla Semi truck unveil set for September. Team has done an amazing job. Seriously next level,” the tweet from Musk’s personal account read, setting off a firestorm of speculation as to what, exactly, the Palo Alto, California, automaker has up its sleeve. Musk’s reputation is such that within the hour, major news outlets were reporting on it, even though Tesla spokespersons decline to comment further.

Musk actually telegraphed his plans for a commercial vehicle last July, in a blog entitled “Master Plan – Part Deux,” posted on the Tesla website. Along with an electric, autonomous commercial vehicle dubbed the “Tesla Semi,” the tycoon and futurist also proposed a fully autonomous, electric compact bus for urban routes along with electric pickup truck and SUV models.

The master plan, released as a blog post on Tesla’s site, lays out the company'’s path beyond the Model 3, with plans for an electric cargo truck equipped with autonomous driving technology called Tesla Semi; a new-style electric bus, smaller than current models, capable of operating without a human driver; a pickup truck; a small SUV. At the time, Musk commented, “We believe the Tesla Semi will deliver a substantial reduction in the cost of cargo transport, while increasing safety and making it really fun to operate.”

Master Plan – Part Deux also details other Tesla projects, and highlights Musk’s vision and mission of revolutionary products that will drive a global transformation away from fossil fuels toward sustainable energy sources. Musk has said publicly that he predicts civilization will eventually “collapse” unless governments and everyday people can be persuaded to move away from carbon-based fuels to renewable energy sources. Additional Tesla products proposed in the Master Plan from July 2017 include a renewable home energy system that uses solar power and new Tesla battery technology, apps that would let Tesla owners rent out their vehicles when they aren’t using them, and various automotive safety systems that Musk says will be “10 times safer” than cars on the road today.

Related: Tesla Master Plan Includes Commercial Trucks