In January, Tesla CEO Elon Musk said he was "very confident" that the company's cars would achieve full Level 5 self-driving autonomy in 2021. However, just 41 days later, it was discovered that one of the company's engineers had presented a less optimistic timeline to California regulators.

The revelation came from an exchange of letters between the California Department of Motor Vehicles and Tesla Autopilot engineer CJ Moore, published by the legal transparency group Plainsite.

"Tesla is currently at Level 2. To move to a higher level of automation, the rate of driver interaction would have to be a million or two million miles."

"Tesla indicated that Elon estimates the rate of improvement when talking about [Level 5] capability. Tesla could not say whether the rate of improvement would reach L5 by the end of the calendar year.

More directly, as found by Ars Technica, the redacted sentence that appears just before this can still be copied and pasted and simply reads: "Eron's tweet does not match engineering reality per CJ." It is unclear which tweet this refers to, as there appears to be no Level 5-related content in Musk's Twitter feed prior to the March 9 release date, but it is possible that something was deleted.

In self-driving car terminology, level 5 is a fully autonomous car, while level 0 is a car that is not automated at all. As the notes suggest, the autopilot feature in Tesla cars is currently at level 2, meaning that it is in the realm of assistance rather than being reliable enough to drive without supervision.

The step up from Level 2 to Level 5 is considerable, and this is not the first time Musk has been overly optimistic about development time; in 2016 he said he believed "autonomous driving is basically a solved problem," and that "it's basically less than two years to fully autonomous driving I think" (although he added that it would take "at least another year" for regulators to approve the technology)

By 2019, Musk revised his estimate to the end of 2020, and he said last year that "no fundamental challenges remain," just "a lot of little issues."

If the memo between regulators and Tesla is to be believed, these small issues may be a bit larger than the CEO anticipated.