Is that a speculative or declarative claim you are making? The word "should" in your post implies... that it hasn't happened yet. Do you have a source?

Their public statements.

First deliveries have been made to employees, first "real" customers will be in november and they are required to hit their initial Amazon requirement by December.

The idea that they have sold 0 is wrong.

I think the concern is that they've delivered zero vehicles (but even then as you say, with the caveat that they've delivered to employees).

I haven't been following Rivian closely, but I was quite impressed by their PR event with Youtube folks recently https://www.youtube.com/watch?v=KGqexebCcUo - it definitely seems like a real, capable vehicle. Add to that their orders from Amazon (and presumably others at some point), and it seems like a plausible company.

Now, whether they have the margins and cash reserves to handle volatile markets / logistical concerns to survive long enough to become a long-term player, I'm not sure.

They spend 1B per year and have 3B cash on hand.

They can survive for 3 years and sell zero cars.