On the Shopify Plus plan, brands get exclusive access to the checkout.liquid file, enabling them to make flexible customizations to Shopify Checkout. However, they need to upgrade Shopify Checkout periodically in order to unlock new checkout features while ensuring any checkout.liquid customizations remain in-tact.
The next checkout upgrade will take place between January 25, 2021 to February 26, 2021. Only shops with checkout.liquid enabled need to perform the upgrade.
Learn more about the checkout upgrade process and view a full list of the new Shopify Checkout features in the Shopify Help Center.