Tesla revealed the Semi back in 2017, and there have been no significant recent updates on its progress.

But Tesla CEO Elon Musk is now pushing to begin "volume production" of the electric semi truck, according to a company memo obtained by CNBC.

In the memo, Musk urged employees to go "all out" on ramping up production, but did not specify a target launch date. He said production of the battery pack and powertrain would take place at Tesla's Nevada Gigafactory, with production of other components "probably occurring in other states."

Tesla did not directly comment on the CNBC report, but when asked on Twitter is the memo was real, Musk answered with a simple "yes."

Prototype for Tesla Semi electric semi-trailer truck

When he unveiled the Tesla Semi at a private event in November 2017, Musk made some lofty claims. He said the truck would have a range of 500 miles when loaded to the 80,000-pound maximum weight allowed under federal highway regulations for Class 8 trucks. He also promised lower operating costs than diesel trucks, with quicker acceleration.

The 500-mile range is about half that of a typical diesel truck, but far beyond what has been achieved with current battery technology. The battery claims have been puzzling from the start, with no other truck maker able to claim the sort of range numbers Tesla has.

Tesla initially got a lot of big names to sign on to test the Semi, including: Wal-Mart, Anheuser-Busch, Pepsi, UPS, and DHL. Since then, there's been no groundswell of Semi sightings for a long time—although at least one prototype has been spotted delivering new Teslas.

Analysts have called Tesla's focus on a long-haul truck misguided—and that the focus should be on shorter-haul trucks due to a greater cost savings and sheer practicality for charging.