When in the game, press the keybind "H," go to settings, and look for Engine Version under the UI section. Click "Show," and it'll be visible at the top right of your screen, allowing your run to be accepted.

The video also shows the steps to enable the engine version and how to play on the experimental server to test future updates. EXPERIMENTAL SERVER RUNS ARE NOT ALLOWED!

Image by Qeutron & video by GhfjSpero