When they released the first game (Apr-15 I believe), they announce the sequel almost straight away (which upset some people despite FIFA and F1 games and their annual cycle being acceptable). At the time they offered everybody the opportunity to pre-buy into the WMD = World of Mass Development - Development forum and build access, it's where the Project C.A.R.S. name came from
Community
Assisted
Racing
Simulator) programme for the new game. Basically, we've had access since then (around 2.5 years now). I haven't played it much until the last few months to be honest as my PC couldn't cope with the sometimes inefficient early development code. The earliest builds were just a single area like a huge playing field with some elevation changes and a jump with stripes of different surfaces created so that they could work out the tech for grip transition and surface types. Amazing process to watch and I hope they do it again...it's been fascinating watching a game grow and to get to play it in various states of development. It will hammer your download cap if you have limits though as there is an almost daily build cycle.
There was also a press build issued by Bandai Namco based on a dev build from July, which is what a lot of these "preview" videos are being made using. It's actually a lot better now than it was then...I absolutely love it