I remember getting an invite at some point late 2014 or early 2015 and doing a few problems but not submitting as I wasn't serious about interviewing. It's nice that you can see if your solutions passed without any requirement to submit your solutions to Google.

By the way — if you go too long without trying one, you get this:

    foobar:~/ tedmiston$ request
    Requesting challenge...
    Your invitation has expired. Search on to try again later.

Edit - Even Google engineers make errors:

    foobar:~/ tedmiston$ status
    Error(400): Bad request.

I submitted feedback on it. Seems like most commands fail with 400 if your invitation is expired.