At the moment Fusion360 is free as described above and Autodesk have said they expect to continue that arrangement.
BUT the terms include these clauses, my bold:
Autodesk reserves the right, from time to time in its sole discretion, to
(1) modify or release subsequent versions of the Service,
(2) impose license keys, authorizations, or other means of controlling access to the Service, and
(3) change or discontinue the Service or the products, functionality or services comprising the Service, limit the availability of a Service to any geographic area or language at any time.
So there's no guarantee that Fusion360 will be free for ever. However, as there are good commercial reasons for making the product available free to amateur and educational users, I would be surprised to see the privilege withdrawn. I've just started my second free year. It's a good tool.
If the possibility of Fusion360 suddenly costing money is a worry, have a look at FreeCAD. Even though it's still in development it works rather well. OK for single parts, the main shortcoming is that it can't do Assemblies and Joints. Despite having Fusion I still use FreeCAD quite often to model single parts because I find it slightly easier to use. But that's probably a personal thing.
Dave