To enable the new modeling experience, go to Home > Models, then select Use the new model experience.
Warning: If your system does not allow cookies, you must enable the new modeling experience for each session.

Once you've enabled the setting, models opened from Home launch in the new modeling experience. You can disable the new modeling experience from the same page.
If you want to temporarily try the new modeling experience before enabling it, select Try the new model experience at the top of the screen in the Classic interface. Your model launches in the new modeling experience in a separate browser tab.