Subtasks - What level is needed?

My company is looking into utilizing our Planner so that multiple people have access to the same plan, but for the team to create subtasks we have to purchase premium plans. What level (1, 3 or 5) is needed to create a subtask? The breakdown found https://www.microsoft.com/en-us/microsoft-365/planner/microsoft-planner-plans-and-pricing does not specify subtasks.