Game is already free. Will be to the end as far as I can tell.
Supporters ($1 a month or higher on Patreon/Subscribestar) get access to tne new updates 3 days earlier. But no extra content or any other paywalled bullshit.
There have been talks of releasing an uncompiled version with all the assets once the game is done, for something between 5 and 15 bucks for people that may want to use the CK assets to mess around and possibly make their own games at some point.