Yes, you can buy the game as a pre-order and get beta access (PC only).
https://www.kingdomcomerpg.com/en/get-the-game
Note that it is currently a fairly rough state. with low performance. The access is not free, but is open to all kickstarters of Knight or higher tier or the equivalent ‘digital purchase’ available on the website now.
You can buy now, or wait and see how the beta develops… or buy once it is released. I’ve had fun with the beta so far, but it is occasionally a bit frustratingly buggy. I always come back to it though, as it is so very nice to just be in the world.