Direct Answer
The official Closed Beta runs August 21–23, 2026. Pre-ordering grants guaranteed access; a smaller group can be admitted randomly through Steam Playtest.
How to get access
Use the official Steam page. Confirm the current pre-order and event conditions before spending money.
Use Steam Playtest when available. The developer states that only a limited random group can enter this way.
Do not treat this as an Open Beta. The announcement calls it a Closed Beta.
Common Problems
Unable to access the test? Check the event dates first, then confirm your Steam account received the relevant access. The original signup process is not described as a guaranteed beta key route.