Cloud Hooks and Cloud Actions do not run in parallel in the same environment. For example, if two deployments target the same environment, any associated Cloud Hooks, such as drush cache-rebuild executes one after the other. This prevents conflicts that could occur when running certain operations simultaneously, helping to safeguard your application's stability and preventing a broken cache.

Cloud Hooks and Cloud Actions run in parallel across different environments. If you deploy to two different environments simultaneously, the Cloud Hooks for each runs at the same time.