@sam does hoplite use kotlin reflection?

Yes, it needs it to inspect the data classes to work out the types

In a multi-module project, I declare one of the inner data classes of the config object in one of the modules, but I'd like to use Masked w/o depending on the library there (I only want it in my config module where I load the configs...), is there a way I can do the same w/o the extra dependency?

Not out of the box. You could just create your own Masked type and then register a loader for it in the module that uses config